Kitsap County is a county in the U.S. state of Washington. As of the 2020 census, its population was 275,611. Its county seat is Port Orchard; its largest city is Bremerton. The county, formed out of King County and Jefferson County on January 16, 1857, is named for Chief Kitsap of the Suquamish Tribe. Originally named Slaughter County, it was soon renamed.

Kitsap County comprises the Bremerton–Silverdale–Port Orchard, WA Metropolitan Statistical Area, which is also included in the Seattle–Tacoma, WA Combined Statistical Area.

The United States Navy is the largest employer in the county, with installations at Puget Sound Naval Shipyard, Naval Undersea Warfare Center Keyport, and Naval Base Kitsap (which comprises former NSB Bangor and NS Bremerton).

Kitsap County is connected to the eastern shore of Puget Sound by Washington State Ferries routes, including the Seattle-Bremerton Ferry, Southworth to West Seattle via Vashon Island, Bainbridge Island to Downtown Seattle, and from Kingston to Edmonds, Washington. Kitsap Transit provides passenger-only fast ferry service between Bremerton and Seattle, Kingston and Seattle, and Southworth and Seattle.

The Kitsap Peninsula was originally acquired by the U.S. Government in three pieces by three treaties negotiated with the Native American tribes:

• The Treaty of Medicine Creek, signed December 26, 1854, ratified March 3, 1855
• The Treaty of Point Elliott, signed January 22, 1855, ratified April 11, 1859
• Point No Point Treaty, signed January 26, 1855, ratified March 8, 1859.

Territorial Governor Isaac Stevens represented the United States in all three negotiations.

When the Washington Territory was organized in 1853, the Kitsap Peninsula was divided between King County to the east and Jefferson County to the west. Official public papers were required to be filed at the county seat, which meant Peninsula business people had to travel to either Seattle or Port Townsend to transact business. On the understanding that they would "bring home a new county," area mill operators George Meigs and William Renton supported the candidacies to the Territorial Legislature of two employees from their respective mills: Timothy Duane Hinckley from Meigs' and S.B. Wilson from Renton's.

Upon arrival in Olympia, the two men introduced bills to create a new county, to be named "Madison". Representative Abernathy from Wahkiakum County proposed an amendment to name it "Slaughter", in recognition of Lt. William Alloway Slaughter, who had been killed in 1855 in the Yakima War. The bill passed as amended. It was signed by Governor Isaac Stevens on January 16, 1857. The county seat would be located in Meigs's mill town at Port Madison.

In Slaughter County's first election on July 13, 1857, voters were given the opportunity to rename the county. The options were "Mill", "Madison" or "Kitsap". Slaughter was not one of the options. Kitsap won by an overwhelming majority.

Kitsap County is home to several major United States Navy facilities, collectively named Naval Base Kitsap, and grew in response to wars and conflicts in the 20th century. Bremerton, the site of the Puget Sound Naval Shipyard, peaked at 80,000 residents during World War II. Naval Submarine Base Bangor was developed in the 1980s to store nuclear weapons for submarines and contributed to the county's population growth during the decade from 147,000 to 190,000.

According to the United States Census Bureau, the county has a total area of 566 square miles (1,470 km), of which 395 square miles (1,020 km) is land and 171 square miles (440 km) (30%) is water. It is the fourth-smallest county in Washington by land area and third-smallest by total area.

In addition to occupying most of the Kitsap Peninsula, Kitsap County includes both Bainbridge Island and Blake Island. According to Puget Sound Partnership, Kitsap county has over 250 miles (400 km) of saltwater shoreline.

The portion of the county north of Silverdale is often referred to as North Kitsap, and the portion south of Bremerton as South Kitsap.

• Island County - northeast
• Snohomish County - east
• King County - east/southeast
• Pierce County - south/southeast
• Mason County - southwest
• Jefferson County - northwest

Historical population

Census	Pop.	Note	%±
1860	544		—
1870	866		59.2%
1880	1,738		100.7%
1890	4,624		166.1%
1900	6,767		46.3%
1910	17,647		160.8%
1920	33,162		87.9%
1930	30,776		−7.2%
1940	44,387		44.2%
1950	75,724		70.6%
1960	84,176		11.2%
1970	101,732		20.9%
1980	147,152		44.6%
1990	189,731		28.9%
2000	231,969		22.3%
2010	251,133		8.3%
2020	275,611		9.7%
2023 (est.)	277,658		0.7%
U.S. Decennial Census 1790–1960 1900–1990 1990–2000 2010–2020

As of the 2020 census, there were 275,611 people, 105,803 households, and 71,548 families living in the county.

As of the 2010 census, there were 251,133 people, 97,220 households, and 65,820 families residing in the county. The population density was 635.9 inhabitants per square mile (245.5/km). There were 107,367 housing units at an average density of 271.9 per square mile (105.0/km). The racial makeup of the county was 82.6% white, 4.9% Asian, 2.6% black or African American, 1.6% American Indian, 0.9% Pacific islander, 1.6% from other races, and 5.8% from two or more races. Those of Hispanic or Latino origin made up 6.2% of the population. In terms of ancestry, 21.3% were German, 14.4% were Irish, 13.8% were English, 7.1% were Norwegian, and 4.2% were American.

Of the 97,220 households, 31.7% had children under the age of 18 living with them, 53.2% were married couples living together, 10.2% had a female householder with no husband present, 32.3% were non-families, and 25.2% of all households were made up of individuals. The average household size was 2.49 and the average family size was 2.97. The median age was 39.4 years.

The median income for a household in the county was $59,549 and the median income for a family was $71,065. Males had a median income of $52,282 versus $38,499 for females. The per capita income for the county was $29,755. About 6.1% of families and 9.4% of the population were below the poverty line, including 11.8% of those under age 18 and 5.3% of those age 65 or over.

• Bainbridge Island
• Bremerton
• Port Orchard (county seat)
• Poulsbo

Kitsap County is generally considered to be a relatively Democratic area, owing to progressivism stemmed from the county's Scandinavian settlers. In the 2016 U.S. presidential election, Democrat Hillary Clinton received 49.05% of the vote to Republican Donald Trump's 38.07%. This Democratic margin widened in 2020, with candidate Joe Biden receiving 56.90% of the vote versus incumbent Trump receiving 38.80%.

On mainland Kitsap County, politics are strongly influenced by working-class Bremerton, which casts moderate margins for Democratic candidates. Unincorporated Kitsap County is a mix of battleground areas. Non-Bremerton parts of incorporated mainland Kitsap County vary, with Silverdale having become a Republican stronghold, Poulsbo marginally Democratic, and Port Orchard consistently electing Republican candidates.

Democrats typically carry the Indian reservations of the area by wide margins; the area around Little Boston (part of the S'Klallam Indian Reservation) regularly votes for Democratic candidates.

The Kitsap County Auditor Website has detailed election results from 1998 to the present. County area political trends can be tracked by analyzing the election precinct data.

United States presidential election results for Kitsap County, Washington

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2020	61,563	38.80%	90,277	56.90%	6,832	4.31%
2016	49,018	38.07%	63,156	49.05%	16,596	12.89%
2012	52,846	42.58%	67,277	54.21%	3,978	3.21%
2008	53,297	42.63%	68,624	54.89%	3,090	2.47%
2004	55,608	46.86%	60,796	51.23%	2,266	1.91%
2000	46,427	45.13%	50,302	48.90%	6,138	5.97%
1996	35,304	38.59%	44,167	48.28%	12,016	13.13%
1992	29,340	33.13%	34,442	38.89%	24,786	27.99%
1988	34,743	49.88%	33,748	48.45%	1,158	1.66%
1984	36,101	54.11%	29,681	44.49%	931	1.40%
1980	29,420	48.79%	20,893	34.65%	9,983	16.56%
1976	23,124	45.56%	25,701	50.64%	1,925	3.79%
1972	25,831	56.84%	17,011	37.43%	2,604	5.73%
1968	14,520	36.47%	22,273	55.94%	3,022	7.59%
1964	10,702	28.38%	26,904	71.34%	108	0.29%
1960	17,459	46.80%	19,662	52.71%	181	0.49%
1956	17,986	47.73%	19,641	52.12%	58	0.15%
1952	16,876	44.89%	20,531	54.61%	189	0.50%
1948	9,869	32.17%	19,538	63.69%	1,271	4.14%
1944	11,224	31.62%	24,016	67.67%	251	0.71%
1940	5,525	28.19%	13,861	70.73%	210	1.07%
1936	3,440	21.04%	12,414	75.94%	493	3.02%
1932	3,465	24.45%	10,002	70.57%	706	4.98%
1928	6,544	62.97%	3,668	35.30%	180	1.73%
1924	3,954	45.19%	490	5.60%	4,306	49.21%
1920	4,989	49.41%	1,350	13.37%	3,759	37.23%
1916	2,638	37.83%	3,479	49.89%	857	12.29%
1912	1,224	20.12%	969	15.93%	3,889	63.94%
1908	1,819	56.12%	850	26.23%	572	17.65%
1904	1,736	69.19%	320	12.75%	453	18.06%
1900	880	58.43%	489	32.47%	137	9.10%
1896	728	48.89%	728	48.89%	33	2.22%
1892	438	34.60%	370	29.23%	458	36.18%

• District 1 (North Kitsap): Christine Rolfes, Democrat; appointed in 2023
• District 2 (South Kitsap): Charlotte Garrido, Democrat; elected in 2008
• District 3 (Central Kitsap): Katie Walters, Democrat; elected in 2022

Bainbridge Island, East Bremerton, Poulsbo and Silverdale

• Sen. Greg Nance (D) - Appointed September 2023 to replace Drew Hansen, who had left to fill vacant senate seat.
• Rep. Tarra Simmons (D) - First elected November 2020.
• Rep. Drew Hansen (D) - Appointed September 2011 to replace Christine Rolfes who had been appointed to the Senate. First elected in November 2012.

Bremerton, Gig Harbor and Port Orchard

• Sen. Emily Randall (D)
• Rep. Spencer Hutchins (R)
• Rep. Michelle Caldier (R)

Bremerton, Shelton and Mason County

• Sen. Drew MacEwan (R)
• Rep. Dan Griffey (R)
• Rep. Travis Couture (R)

• Olympic College

• Bainbridge Island School District
• Bremerton School District
• Central Kitsap School District
• North Kitsap School District
• South Kitsap School District

Kitsap County is connected to the eastern shore of Puget Sound by several Washington State Ferries routes, including the Seattle-Bremerton Ferry, Southworth to West Seattle via Vashon Island, Bainbridge Island to Downtown Seattle, and from Kingston to Edmonds, Washington.

Kitsap Transit provides local transit service within Kitsap County and connects to other transit systems that continue onto the Olympic Peninsula. The agency launched its fast ferry services to Seattle in July 2017, beginning initially with a Bremerton route and later expanding to Kingston in 2018. Fast ferry service to Southworth is expected to begin in 2020.

The county is connected to Jefferson County and the Olympic Peninsula to the west by the Hood Canal Bridge.

A 48-mile-long (77 km) government-owned rail line, the Bangor-Shelton-Bremerton Navy Railroad, runs through the county. It is a branch off the Puget Sound and Pacific Railroad, with its junction at Shelton. At the Bremerton Junction near Gorst a spur follows Highway 3 along the shore of the Sinclair Inlet terminating at the Puget Sound Naval Ship Yard, the other follows Highway 3 along the western shore of Dyes Inlet, servicing Bangor Naval Submarine Base. The Navy had originally intended to use armored trains to transport nuclear missiles to Bangor for the Trident submarines but protesters and a series of court decisions derailed the plan. Today the railroad is primarily used to transport scrap from PSNS.

• Tarn Adams, programmer and game designer, creator of Dwarf Fortress and other games
• Nathan Adrian, swimmer and Olympic gold medalist
• Ben Gibbard, musician
• Richard F. Gordon Jr., naval officer and aviator, test pilot, and NASA astronaut
• Russell Johnson, actor, best known as The Professor on TV's Gilligan's Island.
• James Kelsey, sculptor
• Debbie Macomber, best-selling romance novelist
• Gregg Olsen, best-selling mystery/crime novelist
• Benji Olson, NFL player for Tennessee Titans
• Delilah Rene, radio personality, author and songwriter
• Bree Schaaf, 2010 Winter Olympics competitor in bobsled.
• Aaron Sele, former all-star MLB pitcher.
• Ben Shepherd, bass player of Seattle rock band Soundgarden
• Scott Shipley, slalom canoeist
• Marvin Williams, NBA player for the Atlanta Hawks
• Andrew Wood, lead singer of Seattle rock band Mother Love Bone

Walking Tall with The Rock and Johnny Knoxville was based in Kitsap County, and the City of Port Orchard is the basis for the fictional community of Cedar Cove in the books by Debbie Macomber.

• National Register of Historic Places listings in Kitsap County, Washington

• Bowen, Evelyn T.; Kvelstad, Rangvald; Parfitt, Elnora; Perry, Fredi; Stott, Virginia (1977). Kitsap County: A History: A Story of Kitsap County and its Pioneers (Second Edition, 1981 ed.). Seattle: Dinner & Klein.

• Kitsap County official website
• Kitsap County USGenWeb
• Kitsap Peninsula Visitor and Convention Bureau
• Kitsap Economic Development Alliance
• Kitsap Historical Society and Museum Archived August 19, 2014, at the Wayback Machine