San Diego County (/ˌsæn diˈeɪɡoʊ/ ), officially the County of San Diego, is a county in the southwest corner of the U.S. state of California, next to the Mexican border. As of the 2020 census, the population was 3,298,634; it is the second-most populous county in California and the fifth-most populous in the United States. Its county seat is San Diego, the second-most populous city in California and the eighth-most populous in the United States. It is the southwesternmost county in the 48 contiguous United States, and is a border county. It is home to 18 Indian reservations, the most of any county in the United States. There are 16 military installations of the Navy, Marine Corps, and Coast Guard in the county.

San Diego County comprises the San Diego–Chula Vista–Carlsbad, CA Metropolitan Statistical Area, which is the 17th most populous metropolitan statistical area and the 18th most populous primary statistical area in the United States. San Diego County is also part of the San Diego–Tijuana region, the largest metropolitan area shared between the United States and Mexico. From north to south, San Diego County extends from the southern borders of Orange and Riverside counties to the Mexico–U.S. border and the municipalities of Tijuana and Tecate in Baja California. From west to east, San Diego County stretches from the Pacific Ocean to its boundary with Imperial County, which separated from it in 1907.

San Diego County has more than 70 miles (113 km) of coastline. This forms the most densely populated region of the county, which has a mild Mediterranean to semiarid climate and extensive chaparral vegetation, similar to the rest of the western portion of Southern California. Precipitation and temperature extremes increase to the east, with mountains that receive frost and snow in the winter. These lushly forested mountains receive more rainfall than the average in Southern California, while the desert region of the county lies in a rain shadow to the east, which extends into the Desert Southwest region of North America.

The area which is now San Diego County has been inhabited for more than 12,000 years by the Kumeyaay (also known as 'Iipai-Tiipai or by the historical Spanish name Diegueño), Luiseño, Cupeño, Cahuilla, and the Acjachemen people and their local predecessors.

In 1542, the explorer Juan Rodríguez Cabrillo, who may have been born in Portugal but sailed under the flag of Castile, claimed San Diego Bay for the Spanish Empire, and he named the site San Miguel. In November 1602, Sebastián Vizcaíno surveyed the harbor and what are now Mission Bay and Point Loma and named the area for Saint Didacus, a Spaniard more commonly known as San Diego. European settlement in what is now San Diego County began with the founding of the San Diego Presidio and Mission San Diego de Alcalá by Spanish soldiers and clerics in 1769. This county was part of Alta California under the Viceroyalty of New Spain until the Mexican declaration of independence. From 1821 through 1848, this area was part of Mexico.

San Diego County became part of the United States as a result of the Treaty of Guadalupe Hidalgo in 1848, ending the Mexican–American War. This treaty designated the border to pass through a point one marine league south of the southernmost point of the port of San Diego, ensuring that the United States received all of the natural harbor of San Diego Bay.

San Diego County was one of the original counties of California, created at the time of California statehood in 1850.

At the time of its establishment in 1850, San Diego County was relatively large, and included all of southernmost California south and east of Los Angeles County. It included areas of what are now Inyo and San Bernardino Counties, as well as all of what are now Riverside and Imperial Counties.

During the later part of the 19th century, there were numerous changes in the boundaries of San Diego County, when various areas were separated to make up the counties mentioned above. The most recent changes were the establishments of Riverside County in 1893 and Imperial County in 1907. Imperial County was also the last county to be established in California, and after this division, San Diego no longer extended from the Pacific Ocean to the Colorado River, and it no longer covered the entire border between California and Mexico.

According to the U.S. Census Bureau, the county has an area of 4,526 square miles (11,720 km), of which 4,207 square miles (10,900 km) is land and 319 square miles (830 km) (7.0%) is water. The county is larger in area than the combined states of Rhode Island and Delaware.

San Diego County has a varied topography. On its western side is more than 70 miles (113 km) of coastline. Most of San Diego between the coast and the Laguna Mountains consists of hills, mesas, and small canyons. Snow-capped (in winter) mountains rise to the east, with the Sonoran Desert farther to the east. The Cleveland National Forest is spread across the central portion of the county, while Anza-Borrego Desert State Park occupies most of the northeast.

Although the county's western third is primarily urban, the mountains and deserts in the eastern two-thirds are primarily undeveloped backcountry. Most of these backcountry areas are home to a native plant community known as chaparral. San Diego County contains more than 1,000,000 acres (4,000 km) of chaparral, twice as much as any other California county.

Periodically the area has been subject to wildfires that force thousands to evacuate. The most recent are the December 2017 Lilac Fire, the May 2014 San Diego County wildfires, the Witch Creek Fire in 2007, and the Cedar Fire in 2003. California defines a fire season in which fires are most likely to occur, usually between late July and late October (which are the driest months of the area). Signs posted in numerous spots of the county provide information on the level of threats from fires based on weather conditions.

Northern San Diego County is known as North County; the eastern suburbs are collectively known as East County; the rural areas located further east and extending to the Imperial County line are known as the Mountain Empire; and the southern suburbs, extending to the Mexican border, are collectively known as the South Bay or South County, including South San Diego, an exclave of the city of San Diego which has no land connection to the rest of the city.

San Diego County is bordered on the northwest by Orange County, on the north by Riverside County; on the east by Imperial County; on the south by Mexico; and on the west by the Pacific Ocean.

Under the Köppen climate classification system, the urban and suburban San Diego area straddles areas of Mediterranean climate (Csa) to the north and hot semi-arid climate (BSh) to the south and east. As a result, it is often described as "arid Mediterranean" and "semi-arid steppe." Farther east, arid desert conditions prevail. Western San Diego's climate is characterized by warm, dry summers and mild winters with most of the annual precipitation falling between November and March. The city has mild, mostly dry weather, with an average of 201 days above 70 °F (21 °C) and low rainfall (9–13 inches (23–33 cm) annually). Summer temperatures are generally warm, with average highs of 70–78 °F (21–26 °C) and lows of 55–66 °F (13–19 °C). Temperatures exceed 90 °F (32 °C) only four days a year. Most rainfall occurs from November to April. Winter temperatures are mild, with average high temperatures of 66–70 °F (19–21 °C) and lows of 50–56 °F (10–13 °C).

The climate in the San Diego area, like much of California, often varies significantly over short geographical distances resulting in microclimates. In San Diego's case this is mainly due to the city's topography (the Bay, and the numerous hills, mountains, and canyons). Frequently, particularly during the "May gray/June gloom" period, a thick marine layer will keep the air cool and damp within a few miles of the coast, but will yield to bright cloudless sunshine approximately 5–10 miles (8.0–16.1 km) inland. This happens every year in May and June. Even in the absence of June gloom, inland areas tend to experience much more significant temperature variations than coastal areas, where the ocean serves as a moderating influence. Thus, for example, downtown San Diego averages January lows of 48 °F (9 °C) and August highs of 77 °F (25 °C). The city of El Cajon, just 10 miles (16 km) northeast of downtown San Diego, averages January lows of 42 °F (6 °C) and August highs of 89 °F (32 °C). Julian, in the mountains, has an average January low of 29 °F (−2 °C) and August high of 85 °F (29 °C). Borrego Springs, in the Colorado Desert, has an average January low of 43 °F (6 °C) and August high of 106 °F (41 °C).

Rainfall along the coast averages about 10 inches (25 cm) of precipitation annually, which occurs mainly during the cooler months of December through April. Though there are few wet days per month during the rainy period, rainfall can be heavy when it does occur. However, the rainfall is greater in the higher elevations of San Diego. Some of the higher areas of San Diego, such as Palomar Mountain and the Laguna Mountains, receive 20–40 inches (51–102 cm) of rain per year, supporting lush forests similar to the Sierra Nevada and California Coast Range. The Colorado Desert portion of the county lies to the east of the mountains, which receives the least amount of precipitation; Borrego Springs, the largest population center in the desert, averages only 5 inches (13 cm), with a high evaporation rate.

• Cabrillo National Monument
• Cleveland National Forest (part)
• San Diego National Wildlife Refuge Complex, which includes
  • San Diego National Wildlife Refuge
  • San Diego Bay National Wildlife Refuge
  • Tijuana Slough National Wildlife Refuge
  • Seal Beach National Wildlife Refuge (located in Orange County)

There are seven official wilderness areas in San Diego County that are part of the National Wilderness Preservation System (NWPS). Four of these are integral parts of Cleveland National Forest, whereas three are managed by the Bureau of Land Management (BLM). Some of these extend into neighboring counties (as indicated below):

• Otay Mountain Wilderness (BLM)
• Pine Creek Wilderness (Cleveland National Forest)
• Hauser Wilderness (Cleveland National Forest)
• Carrizo Gorge Wilderness (BLM)
• Sawtooth Mountains Wilderness (BLM)
• Agua Tibia Wilderness (Cleveland National Forest) partly in Riverside County
• San Mateo Canyon Wilderness (Cleveland National Forest) mostly in Riverside County

There are 236 mountain summits and peaks in San Diego County including:

• San Diego River
• San Luis Rey River
• San Dieguito River
• Sweetwater River
• Otay River
• Tijuana River
  • Tijuana River Mouth State Marine Conservation Area
• Santa Margarita River

More than 1,700 tons of radioactive waste are stored at San Onofre Nuclear Generating Station, which sits in an area where there is a record of past tsunamis.

In the 1847 census of San Diego County ordered by Richard Barnes Mason, it found that 2,287 people lived in the county, to include Native Americans, Pacific Islanders, and African Americans. Since at least 2014, San Diego County is the fifth most populous county in the United States. In 2000, only about 3% of San Diego County residents left the county for work while 40,000 people commuted into the metropolitan area.

Historical population

Census	Pop.	Note	%±
1850	798		—
1860	4,324		441.9%
1870	4,951		14.5%
1880	8,018		61.9%
1890	34,987		336.4%
1900	35,090		0.3%
1910	61,665		75.7%
1920	112,248		82.0%
1930	209,659		86.8%
1940	289,348		38.0%
1950	556,808		92.4%
1960	1,033,011		85.5%
1970	1,357,854		31.4%
1980	1,861,846		37.1%
1990	2,498,016		34.2%
2000	2,813,833		12.6%
2010	3,095,313		10.0%
2020	3,298,634		6.6%
2023 (est.)	3,269,973		−0.9%
U.S. Decennial Census 1790–1960 1900–1990 1990–2000 2010 2020

San Diego County, California – Racial and ethnic composition
Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos may be of any race.

Race / Ethnicity (NH = Non-Hispanic)	Pop 1990	Pop 2000	Pop 2010	Pop 2020	% 1990	% 2000	% 2010	% 2020
White alone (NH)	1,633,281	1,548,833	1,500,047	1,422,205	65.38%	55.04%	48.46%	43.11%
Black or African American alone (NH)	149,898	154,487	146,600	145,014	6.00%	5.49%	4.74%	4.40%
Native American or Alaska Native alone (NH)	15,050	15,253	14,098	12,841	0.60%	0.54%	0.46%	0.39%
Asian alone (NH)	185,144	245,297	328,058	400,589	7.41%	8.72%	10.60%	12.14%
Pacific Islander alone (NH)	N/A	12,164	13,504	12,991	N/A	0.43%	0.44%	0.39%
Other race alone (NH)	3,862	5,822	6,715	18,125	0.15%	0.21%	0.22%	0.55%
Mixed race or Multiracial (NH)	N/A	81,012	94,943	167,240	N/A	2.88%	3.07%	5.07%
Hispanic or Latino (any race)	510,781	750,965	991,348	1,119,629	20.45%	26.69%	32.03%	33.94%
Total	2,498,016	2,813,833	3,095,313	3,298,634	100.00%	100.00%	100.00%	100.00%

'

Racial and ethnic composition	2020	2010	2000	1990	1980	1970	1960
White (non-Hispanic)	43.1%	48.5%	55.0%	65.3%	73.8%	–	–
Hispanic or Latino (of any race)	33.9%	32.0%	26.7%	20.4%	14.7%	12.8%	–
Asian (non-Hispanic)	12.1%	10.6%	8.8%	7.9%	–	–	1.1%
Black or African American (non-Hispanic)	4.4%	4.7%	5.7%	6.3%	5.6%	4.5%	3.8%
Native American (non-Hispanic)	0.4%	0.5%	0.8%	0.8%	–	–	0.3%
Pacific Islander (non-Hispanic)	0.4%	0.4%	0.5%	–	–	–	–
Mixed Race (non-Hispanic)	5.1%	3.1%	4.7%	–	–	–	–

Income (2011)
Per capita income	$30,955
Median household income	$63,857
Median family income	$74,633

The 2010 United States census reported that San Diego County had a population of 3,095,313. The racial makeup of San Diego County was 1,981,442 (64.0%) White, 158,213 (5.1%) African American, 26,340 (0.9%) Native American, 336,091 (10.9%) Asian (4.7% Filipino, 1.6% Vietnamese, 1.4% Chinese, 3.2% Other Asian), 15,337 (0.5%) Pacific Islander, 419,465 (13.6%) from other races, and 158,425 (5.0%) from two or more races. Hispanic or Latino of any race were 991,348 people (32.0%). Including those of mixed race, the total number of residents with Asian ancestry was 407,984.

As of 2009, the racial makeup of the county was 79.4% White American, 5.6% Black or African American, 1% Native American, 10.4% Asian, 0.5% Pacific Islander, 10.3% from other races, and 3.6% from two or more races. 31.3% of the population were Hispanic or Latino of any race.

67.0% spoke only English at home; 21.9% spoke Spanish, 3.1% Tagalog and 1.2% Vietnamese.

As of 2018, the Census Bureau estimates there were 3,343,364 people, 1,067,846 households, and 663,449 families residing in the county. The population density was 670 inhabitants per square mile (260/km). There were 1,142,245 housing units at an average density of 248 per square mile (96/km).

In 2000, there were 994,677 households, out of which 33.9% had children under the age of 18 living with them, 50.7% were married couples living together, 11.6% had a female householder with no husband present, and 33.3% were non-families. 24.2% of all households were made up of individuals, and 7.9% had someone living alone who was 65 years of age or older. The average household size was 2.73 and the average family size was 3.29.

As of 2000, 25.7% of the population was under the age of 18, 11.30% was from 18 to 24, 32.0% from 25 to 44, 19.8% from 45 to 64, and 11.2% was 65 years of age or older. The median age was 33 years. For every 100 females, there were 101.2 males. For every 100 females age 18 and over, there were 99.7 males.

In 2012, it was estimated that there were 198,000 unauthorized immigrants; the origin of the plurality of them is Mexico.

In 2018, the median household income was $70,824; most people spend more than 30% of their income on housing costs. In August of that year, the median home price was $583,000; this is lower than the median home price in Los Angeles, and Orange counties.

According to the 2000 census, the median income for a household in the county was $47,067, and the median income for a family was $53,438. Males had a median income of $36,952 versus $30,356 for females. The per capita income for the county was $22,926. About 8.9% of families and 12.4% of the population were below the poverty line, including 16.5% of those under age 18 and 6.8% of those age 65 or over.

Much of the county's high-income residents are concentrated in the northern part of the city of San Diego. The San Diego metropolitan area has two places with both a population of over 50,000 and a per capita income of over $40,000: Carlsbad and Encinitas.

The county's largest continuous high-income urban area is a triangle from a first point on the northern edge of Carlsbad, a second point southeast of Escondido, and a third point on the southern edge of La Jolla. It contains all or most of the cities of Carlsbad, Encinitas, Solana Beach, Del Mar, and Poway in addition to a substantial portion of northern San Diego.

According to a point-in-time count taken for the San Diego Regional Task Force on Homelessness, there were 8,576 homeless individuals on January 6, 2018, a 6% decrease from 2017. 3,586 were sheltered, and 4,990 were not. 4,912 (75.3%) were in the city of San Diego. North County Inland had 1,153 (13.4%), North County Coastal with 822 homeless (9.6%), 602 (7%) were found in South County, and 1,087 (12.7%) in East County.

According to a 2014 Pew Research Center survey, 68% of adults in the county were Christian, of whom 32% were Catholic. 27% were religiously unaffiliated, and 5% adhered to a non-Christian faith. According to the University of Southern California, in 2010, the largest faith in the county was Catholicism, followed by non-denominational Christians, and Mormons.

In 2014, the county had 978 religious organizations, the seventh most out of all US counties.

In 2014 according to Pew Research Center, there are about 170,000 undocumented immigrants living in the region. San Diego has been a destination for trafficked minors from Mexico and the Philippines. In 2018, the United States Border Patrol caught an average of over a hundred individuals crossing the border illegally each day.

San Diego County and Imperial County are part of the Southern Border Region, one of nine such regions. As a regional economy, the Southern Border Region is the smallest but most economically diverse region in the state. However, the two counties maintain weak relations and have little in common aside from their common border. The region has a high cost of living. This includes the highest cost of water in the United States. As of 2018, San Diego County is within the top ten highest cost of rent in the United States; this has led to people moving out of the county.

San Diego County's agriculture industry was worth $1.85 billion in 2013, and is one of the top five egg producing counties in the United States. In 2013, San Diego County also had the most small farms of any county in the United States, and had the 19th largest agricultural economy of any county in the United States. According to the San Diego Farm Bureau, San Diego County is the United States' leading producer of avocados and nursery crops. Until the early 20th century, San Diego County had a thriving wine industry; however the 1916 Charles Hatfield flood was the beginning of the end of the industry which included the destruction of the Daneri winery in Otay Valley. As of October 2016, there are roughly one hundred vineyards and wineries in San Diego County.

By the 2019–2020 statistical survey, California Department of Food & Agriculture (cdfa) found that the nursery trade dominated the county's agriculture by dollar value. Second place went to avocado production.

The county has been called "the Craft Beer Capital of America". Brewing has been one of the fastest-growing business sectors with local breweries ranking among the 50 largest craft brewers in the United States and breweries that are consistently rated among the top breweries in the world.

Commercial operations to grow, test, or sell cannabis are not allowed in the unincorporated areas of the county. Companies must be licensed by the local agency to operate and each city or county may authorize none or only some of these activities. Local governments may not prohibit adults, who are in compliance with state laws, from growing, using, or transporting marijuana for personal use.

Tourism plays a large part in the economics of the San Diego metropolitan area. Tourists are drawn to the region for a well rounded experience, everything from shopping to surfing as well as its mild climate. Its numerous tourist destinations include Westfield UTC, Seaport Village, and Fashion Valley for shopping. SeaWorld San Diego and Legoland California as amusement parks. Golf courses such as Torrey Pines Golf Course and Balboa Park Golf Course. Museums such as the Museum of Us, the San Diego Museum of Art, Fleet Science Center, San Diego Natural History Museum, USS Midway Museum, and the San Diego Air & Space Museum. Historical places such as the Gaslamp Quarter, Balboa Park and Old Town San Diego State Historic Park. Wildlife refuges, zoos, and aquariums such as the San Diego Zoo, San Diego Zoo Safari Park, Birch Aquarium, and the San Diego-La Jolla Underwater Park. Outdoor destinations include the Peninsular Ranges for hiking, biking, mountainboarding and trail riding. Surfing locations include Swami's, Stone Steps Beach, Torrey Pines State Beach, Cardiff State Beach, San Onofre State Beach and the southern portion of Black's Beach.

The region is host to the second largest cruise ship industry in California which generates an estimated $2 million annually from purchases of food, fuel, supplies, and maintenance services. In 2008, the Port of San Diego hosted 252 ship calls and more than 800,000 passengers.

The culture of San Diego is influenced heavily by American and Mexican cultures due to its position as a border town, its large Hispanic population, and its history as part of Spanish America and Mexico. The area's longtime association with the U.S. military also contributes to its culture. Present-day culture includes many historical and tourist attractions, a thriving musical and theatrical scene, numerous notable special events, a varied cuisine, and a reputation as one of America's premier centers of craft brewing.

• Mount Laguna Observatory, owned and primarily operated by San Diego State University
• Palomar Observatory, owned and primarily operated by the California Institute of Technology
• Ramona Valley, a wine-producing region located 28 miles (45 km) northeast of the city of San Diego
• San Diego Zoo Safari Park, formerly known as the San Diego Wild Animal Park, 35 miles (56 km) north of the San Diego Zoo and east of Escondido
• SeaWorld San Diego on Mission Bay.
• Mission Bay Park, including Fiesta Island, a sheltered bay popular for water sports, also known for the annual over-the-line tournament.
• Mission San Diego de Alcalá, the first of California's 21 Spanish missions. It is an operating Roman Catholic parish and also is open for historical interest tours during the week. It is located near the interchange of Interstates 8 and 15.
• Mission San Luis Rey de Francia, founded on June 13, 1798, by Padre Fermín Lasuén. It is the 18th of the Spanish missions established in California. It is an operating Roman Catholic parish and is open every day for historical interest tours. It is located near Route 76 in the Oceanside area.
• Balboa Park, with numerous museums and other cultural locations, just north of Downtown San Diego.
• San Diego Zoo, located in Balboa Park
• Presidio Park, located on a bluff directly above Old Town, a city historic park on the site of the San Diego Presidio, the first European settlement in California.
• San Diego Bay contains the aircraft carrier USS Midway now used as a memorial ship and as a floating museum, and the eight floating museum ships of the Maritime Museum of San Diego. Harbor cruises, sailing, and sport fishing are also available
• San Diego Botanic Garden, a 37-acre botanic oasis in the coastal community of Encinitas. Features 4 miles of meandering trails, 5,300+ plant species and 29 uniquely themed gardens, including the largest public bamboo collection in North America.
• Legoland California, a Lego theme park in Carlsbad
• Sesame Place San Diego, a Sesame Street theme park in Chula Vista
• Alta Vista Botanical Gardens is a botanical garden in Vista dedicated to bringing together 'People, Nature & Art'.
• Mount Ecclesia is a historic district noted for its singular architecture and the preservation of nature grounds and gardens, offering a unique meditative walking experience. It is located about a mile east of Interstate 5 in the Oceanside area.
• San Dieguito County Park

Sports in San Diego County includes major professional league teams, other highest-level professional league teams, minor league teams, and college athletics. San Diego County hosts two teams of the major professional leagues, the San Diego Padres of Major League Baseball (MLB) and San Diego FC of Major League Soccer (MLS). The county is home to several universities whose teams compete in various NCAA Division I sports, most notably the San Diego State Aztecs. The Farmers Insurance Open, a professional golf tournament on the PGA Tour, is played annually at Torrey Pines Golf Course.

San Diego County hosted the National Football League (NFL)'s San Diego Chargers from 1961 to 2017, when the team relocated to the Greater Los Angeles area (now the Los Angeles Chargers). The county also hosted the National Basketball Association (NBA)'s San Diego Rockets from 1967 to 1971 (now the Houston Rockets) and San Diego Clippers from 1978 to 1984 (now the Los Angeles Clippers). San Diego County has never hosted a National Hockey League (NHL) franchise, though it hosted the San Diego Mariners of the now-defunct World Hockey Association (WHA) from 1974 to 1977.

Currently, there is no NFL, NBA, or NHL team in the county. San Diego is the largest American city not to have won a championship in a "Big Four" major professional league. The city does have one major league title to its name: the 1963 American Football League (AFL) Championship won by the San Diego Chargers, when the AFL was an independent entity prior to the AFL–NFL merger in 1970. Due to its lackluster record on winning professional championships, and in some cases retaining professional teams, some San Diego sports fans believe there is a curse on professional sports in the city.

The government of San Diego County is defined and authorized under the Constitution of California, California law, and the Charter of the County of San Diego. Much of the government of California is in practice the responsibility of county governments such as the government of San Diego County. The County government provides countywide services such as elections and voter registration, law enforcement, jails, vital records, property records, tax collection, public health, and social services. In addition the County serves as the local government for all unincorporated areas. Some chartered cities such as San Diego and Chula Vista provide municipal services such as police, public safety, libraries, parks and recreation, and zoning. Other cities such as Del Mar and Vista arrange to have the County provide some or all of these services on a contract basis.

The county government is composed of the elected five-member San Diego County Board of Supervisors, several other elected offices and officers

Office	Official	Party
Clerk	Jordan Marks	Republican
District Attorney	Summer Stephan	Independent
Sheriff	Kelly Martinez	Democratic
Treasurer	Dan McAllister	Republican

and numerous county departments and entities under the supervision of the Chief Administrative Officer such as the Probation Department. In addition, several entities of the government of California have jurisdiction conterminous with San Diego County, such as the San Diego Superior Court.

Under its foundational Charter, the five-member elected Board of Supervisors is the county legislature. The board operates in a legislative, executive, and quasi-judicial capacity. As a legislative authority, it can pass ordinances for the unincorporated areas (ordinances that affect the whole county, like posting of restaurant ratings, must be ratified by the individual city). As an executive body, it can tell the county departments what to do, and how to do it. As a quasi-judicial body, the Board is the final venue of appeal in the local planning process.

As of June 2023, the members of the San Diego County Board of Supervisors are:

District	Supervisor	Party
1	Nora Vargas (Chair)	Democrat
2	Joel Anderson (Chair Pro Tem)	Republican
3	Terra Lawson-Remer (Vice Chair)	Democrat
4	Monica Montgomery-Steppe	Democrat
5	Jim Desmond	Republican

For several decades, ending in 2013, all five supervisors were Republican, white, graduates of San Diego State University, and had been in office since 1995 or earlier. The Board was criticized for this homogeneity, which was made possible because supervisors draw their own district lines and, until 2010, were not subject to term limits.) That pattern was broken in 2013 when Slater-Price retired; she was replaced by Democrat Dave Roberts, who won election to the seat in November 2012 and was inaugurated in January 2013.

The San Diego County Code is the codified law of San Diego County in the form of ordinances passed by the Board of Supervisors. The Administrative Code establishes the powers and duties of all officers and the procedures and rules of operation of all departments.

The county motto is "The noblest motive is the public good." County government offices are housed in the historic County Administration Center Building, constructed in 1935–1938 with funding from the Works Progress Administration.

San Diego County registered voters (2019)
Total population	3,338,330
Registered voters	1,747,383	52.3%
Democratic	623,925	35.7%
Republican	475,149	27.2%
Democratic–Republican spread	+148,776	+8.5%
No party preference	552,538	31.6%
American Independent	55,800	3.2%
Libertarian	16,355	0.9%
Other	11,474	0.7%
Green	6,887	0.4%
Peace and Freedom	5,255	0.3%

With its prominent military presence, San Diego County historically has been a Republican Party stronghold, but in recent years it has come to favor the Democratic Party. The Republican presidential nominee carried the county in every election from 1948 through 2004, except in 1992, when Bill Clinton won a 37% plurality of the vote. In 2008, Barack Obama became the first Democratic presidential candidate to win a majority of votes in San Diego County since World War II. Democratic candidates continued to carry the county in 2012, 2016, 2020 and 2024. Joe Biden's 2020 margin of victory in the county, 22.8%, was the largest for a Democratic candidate since 1936, though it was narrower than Biden's statewide margin of 29.2%.

United States presidential election results for San Diego County, California

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	593,270	40.14%	841,372	56.93%	43,386	2.94%
2020	600,094	37.46%	964,650	60.21%	37,399	2.33%
2016	477,766	36.43%	735,476	56.07%	98,376	7.50%
2012	536,726	44.95%	626,957	52.51%	30,266	2.53%
2008	541,032	43.79%	666,581	53.95%	27,890	2.26%
2004	596,033	52.45%	526,437	46.33%	13,881	1.22%
2000	475,736	49.63%	437,666	45.66%	45,232	4.72%
1996	402,876	45.57%	389,964	44.11%	91,311	10.33%
1992	352,125	35.69%	367,397	37.24%	267,124	27.07%
1988	523,143	60.19%	333,264	38.34%	12,788	1.47%
1984	502,344	65.30%	257,029	33.41%	9,894	1.29%
1980	435,910	60.81%	195,410	27.26%	85,546	11.93%
1976	353,302	55.74%	263,654	41.60%	16,839	2.66%
1972	371,627	61.82%	206,455	34.34%	23,055	3.84%
1968	261,540	56.26%	167,669	36.07%	35,654	7.67%
1964	214,445	50.31%	211,808	49.69%	33	0.01%
1960	223,056	56.41%	171,259	43.31%	1,106	0.28%
1956	195,742	64.47%	106,716	35.15%	1,147	0.38%
1952	186,091	63.50%	105,255	35.92%	1,688	0.58%
1948	101,552	49.43%	98,217	47.80%	5,690	2.77%
1944	75,746	45.42%	89,959	53.94%	1,059	0.64%
1940	55,434	43.27%	71,188	55.57%	1,488	1.16%
1936	35,686	35.04%	64,628	63.45%	1,540	1.51%
1932	35,305	41.46%	45,622	53.58%	4,223	4.96%
1928	47,769	67.14%	22,749	31.97%	633	0.89%
1924	22,726	48.99%	2,944	6.35%	20,721	44.67%
1920	19,826	63.78%	8,478	27.27%	2,783	8.95%
1916	16,978	46.47%	16,815	46.02%	2,744	7.51%
1912	63	0.29%	9,731	44.79%	11,934	54.92%
1908	5,412	57.56%	2,393	25.45%	1,598	16.99%
1904	4,303	59.52%	1,398	19.34%	1,529	21.15%
1900	3,800	54.91%	2,678	38.69%	443	6.40%
1896	3,631	46.86%	3,908	50.44%	209	2.70%
1892	3,525	45.71%	2,334	30.26%	1,853	24.03%
1888	4,661	56.88%	3,189	38.92%	344	4.20%
1884	1,120	57.00%	800	40.71%	45	2.29%
1880	743	56.80%	546	41.74%	19	1.45%

The city of San Diego itself is more Democratic than the county average and has largely voted Democrat in each presidential election since 1992; certain areas and cities within the county are swing areas and have split their votes in post-2000 elections. The county's Republican population gradually increases the further one travels away from downtown; the Republican strongholds include La Jolla, Coronado, the regions of North and East County, the eastern backlands, and remote mountain communities such as Julian. While these areas have traditionally voted Republican, all also contain varied electorates of Democrats, Libertarians, and independents.

A unique feature of the political scene is the use of Golden Hall, a convention facility next to San Diego's City Hall. The County Registrar of Voters rents the hall to distribute election results. Supporters and political observers gather to watch the results come in; supporters of the various candidates parade around the hall, carrying signs and chanting; candidates give their victory and concession speeches and host parties for campaign volunteers and donors at the site; and television stations broadcast live from the floor of the convention center. The atmosphere at Election Central on the evening of election day has been compared to the voting portion of a political party national convention.

On November 4, 2008, San Diego County voted 53.71% for Proposition 8, which amended the California Constitution, effectively placing a ban on same-sex marriages; this proposition would restore Proposition 22, which was overturned by a ruling from the California Supreme Court. However, the City of San Diego, along with the North County coastal cities of Del Mar, Encinitas, and Solana Beach voted against Proposition 8. La Mesa was a virtual tie for Prop. 8 support, while Carlsbad supported the referendum by only a 2% margin.

In the U.S. House of Representatives, San Diego County is split between five congressional districts:

• California's 48th congressional district, represented by Republican Darrell Issa
• California's 49th congressional district, represented by Democrat Mike Levin
• California's 50th congressional district, represented by Democrat Scott Peters
• California's 51st congressional district, represented by Democrat Sara Jacobs and
• California's 52nd congressional district, represented by Democrat Juan Vargas.

In the California State Assembly, San Diego County is split between seven legislative districts:

• the 71st Assembly District, represented by Republican Kate Sanchez,
• the 75th Assembly District, represented by Republican Carl DeMaio,
• the 76th Assembly District, represented by Democrat Darshana Patel,
• the 77th Assembly District, represented by Democrat Tasha Boerner,
• the 78th Assembly District, represented by Democrat Chris Ward,
• the 79th Assembly District, represented by Democrat LaShae Sharp-Collins, and
• the 80th Assembly District, represented by Democrat David Alvarez.

In the California State Senate, San Diego County is split between four legislative districts:

• the 36th Senate District, seat currently vacant,
• the 38th Senate District, represented by Democrat Catherine Blakespear,
• the 39th Senate District, represented by Democrat Akilah Weber, and
• the 40th Senate District, represented by Republican Brian Jones.

The following table includes the number of incidents reported and the rate per 1,000 persons for each type of offense.

Population and crime rates
Population	3,060,849
Violent crime	12,775	4.17
Homicide	75	0.02
Forcible rape	746	0.24
Robbery	4,033	1.32
Aggravated assault	7,921	2.59
Property crime	43,525	14.22
Burglary	14,522	4.74
Larceny-theft	41,278	13.49
Motor vehicle theft	13,938	4.55
Arson	394	0.13

Cities by population and crime rates
City	Population	Violent crimes	Violent crime rate per 1,000 persons	Property crimes	Property crime rate per 1,000 persons
Carlsbad	107,879	265	2.46	2,109	19.55
Chula Vista	249,830	581	2.33	5,081	20.34
Coronado	19,345	20	1.03	504	26.05
Del Mar	4,263	15	3.52	211	49.50
El Cajon	101,864	365	3.58	2,414	23.70
Encinitas	60,960	150	2.46	1,296	21.26
Escondido	147,386	628	4.26	3,887	26.37
Imperial Beach	26,956	147	5.45	471	17.47
La Mesa	58,444	224	3.83	1,732	29.64
Lemon Grove	25,932	137	5.28	434	16.74
National City	59,920	371	6.19	1,863	31.09
Oceanside	171,141	728	4.25	4,289	25.06
Poway	48,968	94	1.92	559	11.42
San Diego	1,338,477	5,529	4.13	31,700	23.68
San Marcos	85,810	227	2.65	1,502	17.50
Santee	54,700	154	2.82	1,109	20.27
Solana Beach	13,181	24	1.82	313	23.75
Vista	96,087	465	4.84	1,885	19.62

San Diego County contains three public state universities: University of California, San Diego (UC San Diego); San Diego State University (SDSU); and California State University, San Marcos (CSUSM). Major private universities in the county include University of San Diego (USD), Point Loma Nazarene University (PLNU), Alliant International University (AIU), and National University. It also includes three law schools, the USD School of Law, California Western School of Law, and the Thomas Jefferson School of Law.

Within the county there are 24 public elementary school districts, 6 high school districts, and 12 unified school districts. There are also five community college districts.

Several cities in the county maintain public library systems, including the city of San Diego itself. The San Diego County Library serves all other areas of the county. In 2010 the county library had 33 branches and two bookmobiles; circulated over 10.7 million books, CDs, DVDs, and other material formats; recorded 5.7 million visits to library branches; and hosted 21,132 free programs and events. The San Diego County Library is one of the 25 busiest libraries in the nation as measured by materials circulated.

• Grossmont–Cuyamaca Community College District
• MiraCosta Community College District
• Palomar Community College District
• San Diego Community College District
• Southwestern Community College District

School districts

K-12 unified:

Secondary:

Elementary:

San Diego is the headquarters of the U.S. Navy's Eleventh Naval District and is the Navy's principal location for West Coast and Pacific Ocean operations. Naval Base San Diego is principal home to the Pacific Fleet (although the headquarters is located in Pearl Harbor). NAS North Island is located on the north side of Coronado, and is home to Headquarters for Naval Air Forces and Naval Air Force Pacific, the bulk of the Pacific Fleet's helicopter squadrons, and part of the West Coast aircraft carrier fleet.

The Naval Special Warfare Center is the primary training center for SEALs, and is also located on Coronado. The area contains five major naval bases and the U.S. Marines base Camp Pendleton. Marine Corps Base Camp Pendleton is the major West Coast base of the United States Marine Corps and serves as its prime amphibious training base. It is located on the Southern California coast, bordered by Oceanside to the south, San Clemente to the north, and Fallbrook to the east.

• Naval Base San Diego, also known as 32nd Street Naval Station
• Naval Amphibious Base Coronado
• Naval Air Station North Island
• Naval Base Point Loma, which includes the Submarine Base and the Fleet Antisubmarine Warfare Training Center
• Naval Information Warfare Systems Command (NAVWAR)
• Naval Medical Center San Diego, also known as Bob Wilson Naval Hospital and Balboa Naval Hospital

• Marine Corps Base Camp Pendleton
• Marine Corps Air Station Miramar
• Marine Corps Recruit Depot San Diego

• Coast Guard Air Station San Diego

• San Diego Air National Guard Station, which is home to the 147th Combat Communications Squadron.

San Diego County is primarily served by media in San Diego, including TV and radio stations based in the city.

San Diego County is served by many newspapers. The major regional paper is The San Diego Union-Tribune, also known as U-T San Diego or just "The U-T" by locals, is ranked 23rd in the country (by daily circulation) as of March 2013. The Union-Tribune serves both San Diego County and neighboring Imperial County. The former North County Times, based in Escondido and serving portions of Riverside County and North County, was purchased by the Union-Tribune in 2012 and closed down. For about a year after absorbing the North County Times the Union-Tribune published a North County edition, but the regional edition was later abandoned. The Los Angeles Times is also delivered in portions of the county. Many of the area's cities, towns and neighborhoods have their own local newspapers; the Union Tribune bought eight local weeklies in 2013 and is continuing to publish them as independent local newspapers. The San Diego Daily Transcript reports business and legal news. Privately published papers like the Military Press Newspaper and the Navy Dispatch serve the military community both on and off base.

County Television Network is a public-access television cable channel, offering a "hometown blend of C-SPAN, the Lifetime, History, Travel, and Discovery channels" for the county, and funded by fees paid by cable companies.

• San Ysidro Port of Entry
• Otay Mesa Port of Entry
• Otay Mesa East Port of Entry (projected opening 2028)
• Tecate Port of Entry

v t e San Diego County
Legend
Station diagram
Metrolink to Los Angeles & San Bernardino Amtrak to San Luis Obispo Oceanside Coast Highway Crouch Street Carlsbad Village El Camino Real Rancho Del Oro College Boulevard Carlsbad Poinsettia Melrose Drive Vista Civic Center–Vista Buena Creek Encinitas Palomar College San Marcos Civic Center Cal State San Marcos Solana Beach Nordahl Road Escondido Sorrento Valley UC San Diego Central Campus UC San Diego Health La Jolla VA Medical Center Executive Drive Nobel Drive UTC Balboa Avenue Clairemont Drive Tecolote Road Morena/Linda Vista Old Town Fashion Valley Washington Street Hazard Center Middletown County Center/Little Italy Mission Valley Center Santa Fe Depot America Plaza Rio Vista Courthouse Civic Center Fifth Avenue Fenton Parkway City College Park & Market Stadium Seaport Village Convention Center Mission San Diego Gaslamp Quarter Grantville 12th & Imperial SDSU Storage & Maintenance Yard UC San Diego Health East Barrio Logan Harborside 25th & Commercial Pacific Fleet 32nd & Commercial 8th Street 47th Street 24th Street Euclid Avenue E Street Encanto/62nd Street H Street Massachusetts Avenue Palomar Street Lemon Grove Depot Palm Avenue Spring Street Iris Avenue La Mesa Blvd. Beyer Blvd. 70th Street San Ysidro Grossmont Amaya Drive El Cajon Arnele Avenue Gillespie Field Santee

• (Amtrak) Pacific Surfliner
• Coaster
• Metrolink
• San Diego and Arizona Eastern Railway
• San Diego and Imperial Valley Railroad

• San Diego Trolley
• San Diego Metropolitan Transit System (MTS)
• Sprinter
• North County Transit District (NCTD)

• Embarcadero

• McClellan–Palomar Airport (CRQ)

• Gillespie Field (SEE)

• Oceanside Municipal Airport (OKB)

• San Diego International Airport (SAN)
• Montgomery-Gibbs Executive Airport (MYF)
• Brown Field Municipal Airport (SDM)

• Agua Caliente Airport (L54)
• Borrego Valley Airport (L08)
• Fallbrook Community Airpark (L18)
• Jacumba Airport (L78)
• Ocotillo Airport (L90)
• Ramona Airport (RNM)

As of the 2020 census, San Diego County includes 18 incorporated cities, 18 Indian reservations, and 39 census-designated places.

City	Date incorporated	Population (2020 Census)
Carlsbad	July 16, 1952	114,746
Chula Vista	November 28, 1911	275,487
Coronado	December 11, 1890	20,192
Del Mar	July 15, 1959	3,954
El Cajon	Nov 12, 1912	106,215
Encinitas	October 1, 1986	62,007
Escondido	October 8, 1888	151,038
Imperial Beach	July 18, 1956	26,137
La Mesa	February 16, 1912	61,121
Lemon Grove	July 1, 1977	27,627
National City	September 17, 1887	56,173
Oceanside	July 3, 1888	174,068
Poway	December 1, 1980	48,841
San Diego (county seat)	March 27, 1850	1,386,932
San Marcos	January 28, 1963	94,833
Santee	December 1, 1980	60,037
Solana Beach	July 1, 1986	12,941
Vista	January 28, 1963	98,381

San Diego County has 18 federally recognized Indian reservations, more than any other county in the United States. Although they are typical in size to other Indian reservations in California (many of which are termed "Rancherías"), they are relatively small by national standards, and all together total 200.2 sq mi (519 km) of area.

The population ranking of the following table is based on the 2020 census of San Diego County.

† county seat

Rank	City/Town/etc.	Municipal type	Population (2020 Census)	Population (2010 Census)
1	San Diego †	City	1,386,932	1,307,402
2	Chula Vista	City	275,487	243,916
3	Oceanside	City	174,068	167,086
4	Escondido	City	151,038	143,911
5	Carlsbad	City	114,746	105,328
6	El Cajon	City	106,215	99,478
7	Vista	City	98,381	93,834
8	San Marcos	City	94,833	83,781
9	Encinitas	City	62,007	59,518
10	La Mesa	City	61,121	57,065
11	Santee	City	60,037	53,413
12	National City	City	56,173	58,582
13	Poway	City	48,841	47,811
14	La Presa	CDP	35,033	34,169
15	Fallbrook	CDP	32,267	30,534
16	Spring Valley	CDP	30,998	28,205
17	Lemon Grove	City	27,627	25,320
18	Imperial Beach	City	26,137	26,324
19	Winter Gardens	CDP	22,380	20,631
20	Rancho San Diego	CDP	21,858	21,208
21	Ramona	CDP	21,468	20,292
22	Lakeside	CDP	21,152	20,648
23	Coronado	City	20,192	18,912
24	Casa de Oro-Mount Helix	CDP	19,576	18,762
25	Bostonia	CDP	16,882	15,379
26	Alpine	CDP	14,696	14,236
27	Solana Beach	City	12,941	12,867
28	Bonita	CDP	12,917	12,538
29	Camp Pendleton South	CDP	12,468	10,616
30	San Diego Country Estates	CDP	10,395	10,109
31	Valley Center	CDP	10,087	9,277
32	Camp Pendleton Mainside	CDP	9,683	5,200
33	Jamul	CDP	6,179	6,163
34	Eucalyptus Hills	CDP	5,517	5,313
35	Lake San Marcos	CDP	5,328	4,437
36	Bonsall	CDP	4,546	3,982
37	Hidden Meadows	CDP	4,484	3,485
38	Harbison Canyon	CDP	4,048	3,841
39	Del Mar	City	3,954	4,161
40	Granite Hills	CDP	3,267	3,035
41	Rancho Santa Fe	CDP	3,156	3,117
42	Borrego Springs	CDP	3,073	3,429
43	Fairbanks Ranch	CDP	3,002	3,148
44	Campo	CDP	2,955	2,684
45	Crest	CDP	2,828	2,593
46	Harmony Grove	CDP	2,079	N/A
47	Rainbow	CDP	1,884	1,832
48	Julian	CDP	1,768	1,502
49	Pine Valley	CDP	1,645	1,510
50	Pala Indian Reservation	AIAN	1,541	1,315
51	Descanso	CDP	1,499	1,423
52	Pala	CDP	1,490	N/A
53	San Pasqual Reservation	AIAN	1,270	1,097
54	Rincon Reservation	AIAN	1,095	1,215
55	Barona Reservation	AIAN	756	640
56	Potrero	CDP	648	656
57	Elfin Forest	CDP	600	N/A
58	Jacumba	CDP	540	561
59	Viejas Reservation	AIAN	538	520
60	Campo Indian Reservation	AIAN	398	362
61	Del Dios	CDP	396	N/A
62	Boulevard	CDP	359	315
63	Santa Ysabel Reservation	AIAN	263	330
64	Sycuan Reservation	AIAN	218	211
65	Pauma and Yuima Reservation	AIAN	179	206
66	La Jolla Reservation	AIAN	145	476
67	Manzanita Reservation	AIAN	101	78
68	Mesa Grande Reservation	AIAN	87	98
69	Mount Laguna	CDP	74	57
70	La Posta Indian Reservation	AIAN	50	55
71	Los Coyotes Reservation	AIAN	15	98
72	Ewiiaapaayp Reservation	AIAN	5	N/A
	Capitan Grande Reservation	AIAN	0	0
	Inaja and Cosmit Reservation	AIAN	0	0
	Jamul Indian Village	AIAN	0	N/A

City	Year incorporated	Year removed	Fate
East San Diego	1912	1923	Merged into San Diego
Elsinore (now Lake Elsinore)	1888	1893	Riverside County formed
Imperial	1904	1907	Imperial County formed
Riverside	1883	1893	Riverside County formed
San Jacinto	1888	1893	Riverside County formed

The communities of Del Dios, Elfin Forest, Harmony Grove, and Pala were newly-designated as CDPs in the 2020 census.

Some CDPs and unincorporated communities of San Diego County have explored incorporating as cities/towns in the past (California makes no legal distinction between the titles of "city" and "town", allowing communities that incorporate to chose their designation, though there has never been an incorporated town in San Diego County). Alpine, Bonita, Fallbrook, Lakeside, Ramona, Rancho Santa Fe and Spring Valley have each been tied to various incorporation studies, organized efforts and discussions in the past. Some of these past efforts have culminated in ballot initiatives. Voters in Fallbrook previously rejected incorporation in 1981 and 1987. Rancho Santa Fe residents also rejected incorporation in 1987. Among the existing cities of San Diego County, some had multiple failed incorporation efforts before ultimately succeeding in becoming a city. Lemon Grove, for example, saw incorporation measures fail in 1955, 1958 and 1964 before a successful incorporation vote in 1977. Other cities have seen incorporation success thanks to mergers of neighboring unincorporated communities. Encinitas, for example, became an incorporated city through a consolidated effort between the then-unincorporated communities of Cardiff-by-the-Sea, Leucadia, Encinitas and Olivenhain in 1986. Encinitas and Solana Beach in 1986 are the most recent examples of successful campaigns for incorporation within the County of San Diego.

• List of breweries in San Diego County, California
• List of high schools in San Diego County, California
• List of media set in San Diego County, California
• List of museums in San Diego County, California
• List of school districts in San Diego County, California
• List of United States counties and county-equivalents
• National Register of Historic Places listings in San Diego County, California
• San Diego Association of Governments (SANDAG)

• Pryde, Philip R. San Diego: An Introduction to the Region (4th ed. 2004), a historical geography

• Official website
• San Diego Association of Governments (SANDAG) official website
• San Diego Tourism Authority
• San Diego Geographic Information Source