Sussex County (/ˈsʌsɪks/) is the northernmost county in the U.S. state of New Jersey. Its county seat is Newton. It is part of the New York metropolitan area and is part of New Jersey's Skylands Region. As of the 2020 census, the county was the state's 17th-most-populous county, with a population of 144,221, a decrease of 5,044 (−3.4%) from the 2010 census count of 149,265, which in turn reflected an increase of 5,099 (+3.5%) over the 144,166 persons at the 2000 census. Based on 2020 census data, Vernon Township was the county's largest in both population and area, with a population of 22,358 and covering an area of 70.59 square miles (182.8 km). The county is part of the North Jersey region of the state.

In 2015, the county had a per capita personal income of $55,497, the ninth-highest in New Jersey and ranked 220th of 3,113 counties in the United States. As of 2010 The Bureau of Economic Analysis ranked the county as having the 131st-highest per capita income ($49,207) of the 3,113 counties in the United States (and the ninth-highest in the state).

The county was established in 1753 from portions of Morris County and named after the county of Sussex in England.

The area of Sussex County and its surrounding region was occupied for approximately 8,000-13,000 years by succeeding cultures of indigenous peoples. The Munsee Indians inhabited the region at the time of European encounter. The Munsee were a loosely organized division of the Lenape (or Lenni Lenape), a Native American people also called "Delaware Indians" after their historic territory along the Delaware River. The Lenape inhabited the Mid-Atlantic coastal areas and inland along the Hudson and Delaware rivers. The Munsee spoke a very distinct dialect of the Lenape and inhabited a region bounded by the Hudson River, the headwaters of the Delaware River and the Susquehanna River, and south to the Lehigh River and Conewago Creek. As a result of disruption following the French and Indian War (1756–1763), the American Revolutionary War (1775–1783), and later Indian removals from the eastern United States, the main Lenape groups now live in Ontario in Canada, and in Wisconsin and Oklahoma in the United States.

As early as 1690, Dutch and French Huguenot colonists from towns along the Hudson River Valley in New York began permanently settling in the Upper Delaware Valley (known as the "Minisink"). The route these Dutch settlers had taken was the path of an old Indian trail and became the route of the Old Mine Road and stretches of present-date U.S. Route 209. These Dutch settlers penetrated the Minisink Valley and settled as far south as the Delaware Water Gap, by 1731 this valley had been incorporated as Walpack Precinct. Throughout the 18th century, immigrants from the Rheinland Palatinate in Germany and Switzerland fled religious wars and poverty to arrive in Philadelphia and New York City. Several German families began leaving Philadelphia to settle along river valleys in Northwestern New Jersey and Pennsylvania's Lehigh Valley in the 1720s, spreading north into Sussex County in the 1740s and 1750s as additional German emigrants arrived. Also during this time, Scottish settlers from Elizabethtown and Perth Amboy, and English settlers from these cities, Long Island, Connecticut and Massachusetts, came to New Jersey and moved up the tributaries of the Passaic and Raritan rivers, settling in the eastern sections of present-day Sussex and Warren counties.

By the 1750s, residents of this area began to petition colonial authorities for a new county to be formed; they complained of the inconvenience of long travel to conduct business with the government and the courts. By this time, four large townships had been created in this sparsely populated Northwestern region: Walpack Township (before 1731), Greenwich Township (before 1738), Hardwick Township (1750) and Newtown Township (1751). On June 8, 1753, Sussex County was created from these four municipalities, which had been part of Morris County when Morris stretched over all of northwestern New Jersey. Sussex County at this time encompassed present-day Sussex and Warren Counties and its boundaries were drawn by the New York-New Jersey border to the north, the Delaware River to the west, and the Musconetcong River to the south and east. After several decades of debate over where to hold the sessions of the county's courts, the state legislature eventually voted to divide Sussex County in two, using a line drawn from the juncture of the Flat Brook and Delaware River in a southeasterly direction to the Musconetcong River running through the Yellow Frame Presbyterian Church in present-day Fredon Township (then part of Hardwick). On November 20, 1824, Warren County was created from the southern territory of the Sussex County.

Throughout the 18th, 19th, and 20th centuries, Sussex County's economy was largely centered around agriculture and the mining of iron and zinc ores. Early settlers established farms whose operations were chiefly focused towards subsistence agriculture. Because of geological constraints, Sussex County's agricultural production was centered around dairy farming. Several farms had orchards—typically apples and peaches—and surplus fruit and grains were often distilled or brewed into alcoholic beverages (hard ciders, applejack and fruit brandies). This was the economic model until the mid-19th century when advances in food preservation and the introduction of railroads (e.g. the Sussex Railroad) into the area allowed Sussex County to transport farm products throughout the region. Railroads also promoted the building of factories as companies relocated to the area at the end of the 19th century—including that of the H.W. Merriam Shoe Company (1873) in Newton.

The Highlands Region of Northwestern New Jersey has proven to possess rich deposits of iron ore. In the mid 18th century, several entrepreneurial colonists began mining iron in area around Andover, Hamburg, and Franklin present-day Sussex County and establishing forges and furnaces to create pig iron and bar iron. During the American Revolution, the Quartermaster Department of the Continental Army complained to Congress of difficulties in acquiring iron to support the war effort and the Congress ordered two colonels, Benjamin Flower and Thomas Maybury to take possession of the iron works at Andover in order to equip General Washington's army. During the middle of the 19th century, under the management of Cooper and Hewitt, the Andover mine produced 50,000 tons of iron ore each year. The firm manufactured railroad rails and the country's first structural steel, which and led to the building of railroads and commercial development in the county. Iron from the Andover mines was fashioned into cable wire for the bridge built at Niagara Falls and for the beams used to rebuild Princeton University's Nassau Hall in Princeton, New Jersey after a fire undermined the structure in 1855. During the American Civil War, Andover iron found its way into rifle barrels and cannonballs just as it had during the Revolution years before.

As deposits were depleted, the iron mining industry began to diminish by the mid-19th century. During the late 19th century, prolific American inventor Thomas Edison began to explore the commercial opportunities of processing poor-quality low-grade iron ore to combat the growing scarcity of iron deposits in the United States. He began to purchase mining companies in Sussex County in the 1880s and consolidating their assets. He developed a process of crushing and milling iron-bearing minerals and separating iron ore from the material through large electromagnets, and built one of the world's largest ore-crushing mills near Ogdensburg. Completed in 1889, the factory contained three giant electromagnets and was intended to process up to 1200 tons of iron ore every day. However, technical difficulties repeatedly thwarted production. However, in the 1890s, richer soft-grade iron ore deposits located in Minnesota's Iron Range rendered Edison's Ogdensburg operation unprofitable and he closed the works in 1900. Edison adapted the process and machinery for the cement industry and invested in producing Portland Cement in other locations.

In the early 19th century, Samuel Fowler (1779–1844) settled in Franklin Furnace (now Franklin) to open up a medical practice, but is largely known for his interest in mineralogy which led to his developing commercial uses for zinc and for discovery of several rare minerals (chiefly various ores of zinc). Many of these zinc minerals are known for fluorescing in vivid colors when exposed to ultraviolet light. Because of both the rich deposits and many of these minerals are not found anywhere else on earth, Franklin is known as the "Fluorescent Mineral Capitol of the World." Fowler, who later briefly served in elected political office, operated the local iron works and bought several abandoned zinc and iron mines in the area. Shortly after his death, two companies were created to exploit the iron and zinc deposits in this region; they acquired the rights to Fowler's holdings in Franklin and nearby Sterling Hill. These companies later merged to form the New Jersey Zinc Corporation (today known as Horsehead Industries). At this time, Russian, Chilean, British, Irish, Hungarian and Polish immigrants came to Franklin to work in the mines, and the population of Franklin swelled from 500 (in 1897) to over 3,000 (in 1913). Declining deposits in the Franklin area, the expense of pumping groundwater from mine shafts, tax disputes and misdirected investments by the company led to the abandonment of the mines. Today, both the Franklin and Sterling Hill mines are operated as museums.

Beginning in the 1950s and 1960s, construction or improvements of Interstate 80, Route 181 and Route 23 triggered rapid growth to Sussex County. Since 1950, the population nearly quadrupled from 34,423 people to 130,943 people in 1990. This has caused Sussex County to begin developing into a light suburban atmosphere, instead of the sparsely populated rural region it once was, especially in the eastern half of the county.

Around 450 million years ago, the Martinsburg Shale was uplifted when a chain of volcanic islands collided with proto North America. These islands slid over the North American plate, and deposited rock on top of the plate, forming the Highlands and Kittatinny Valley. At that time the western part of Sussex County was under a shallow inland sea. Fossils of sea shells and fish can be found west of the Kittatinny ridge. Then approximately 400 million years ago, a small, narrow continent collided with North America. Pressure from the collision, created heat in the bed rock which folded and faulted the Silurian Shawangunk Conglomerate that was under the shallow sea. The pressure created intense heat, melted the quartzite, and allowed it to bend, creating an uplift. as cooling occurred this cemented the quartz pebbles and conglomerate together. This is how the Kittatinny Ridge was created. The strike from this continent was from the south east, this is why the Kittatinny ridge is on a northeast–southwest axis. The Wisconsin glacier which covered the entire county from 23,000B.C to 13,000 B.C. created many lakes and streams. The glacier covered Kittatinny mountain.

As climate warmed around 13,000 B.C., the area was first a tundra with lichens and mosses. After a few thousand years, coniferous forests began to grow. As climate grew warmer around 8000 B.C., deciduous forests began to grow with nut trees such as oak, and maple. Around 3000 B.C. other nut bearing trees began to grow such as hickory, butternut, walnut and beech. This allowed the Paleo Indian populations to increase. The county is drained by the Paulinskill River, the Flatbrook, which drain into the Delaware River, the Wallkill River which flows north to the Hudson River. There are many smaller creeks that drain into these water sheds.

Sussex County is located within two of New Jersey's physiographic provinces: (1) The Ridge and Valley Appalachians, and (2) the New York-New Jersey Highlands regions.

The features of the Ridge and Valley province were created approximately 400 million years ago during the Ordovician period and Appalachian orogeny— by a continent striking North America the creating Kittatinny Mountain, Blue Mountain, and the Appalachian Mountains. This physiographic province occupies approximately two-thirds of the county's area (the county's western and central sections) dominated by Kittatinny Mountain and the Kittatinny Valley. This province's contour is characterized by long, even ridges with long, continuous valleys in between that generally run parallel from southwest to northeast. This region is largely formed by sedimentary rock.

The New York-New Jersey Highlands, or Highlands region, located in the county's eastern section is older. An extension of the Reading Prong formation stretching from Pennsylvania to Connecticut, the Highlands were created from geological forces created from when a small continent went over the North American plate. This rock created the highlands of Sussex County. Precambrian igneous and metamorphic rock approximately 500 million years ago. The watersheds within the Highlands provide fresh water resources for millions of residents in New Jersey and the New York City Metropolitan Area. Because of this, the region was protected by the New Jersey Legislature and Governor Jim McGreevey under the Highlands Water Protection and Planning Act enacted in 2004. This act sought to protect these water resources from development by promoting open space and farmland preservation, creating new recreational parks, and consolidating the regulatory authority over land use planning in a regional planning commission known as the Highlands Council.

The Delaware River forms the western and northwestern boundary of Sussex County. This region is known as the Upper Delaware Valley and historically as the Minisink or Minisink Valley. Elevations in the regions along the river range from 300 to 500 feet.

Kittatinny Mountain is the dominant geological feature in the western section of the county. It is part of the Appalachian Mountains, and part of a ridge that continues as the Blue Mountain in Eastern Pennsylvania, and as Shawangunk Ridge in New York to the north. It begins in New Jersey as the eastern half of the Delaware Water Gap, and runs northeast to southwest along the Delaware River. Elevations range from 1,200 to 1,800 feet (370 to 550 m) and attains a maximum elevation of 1,803 feet (550 m) at High Point, in Montague Township. Between Kittatinny Mountain and the Delaware River is the Wallpack Ridge, a smaller, narrow ridge spanning 25 miles (40 km) in length from the Walpack Bend near Flatbrookville north to Port Jervis, New York. Wallpack Ridge encloses the watershed of the Flat Brook and its two main tributaries Little Flat Brook and Big Flat Brook, and ranges in elevation from 500 to 900 feet (150 to 270 m) and reaching its highest elevation at 928 feet (283 m).

The Kittatinny Valley lies to the east of Kittatinny Mountain and ends with the Highlands in the east. It is largely a region of rolling hills and flat valley floors. Elevations in this valley range from 400 to 1,000 feet. It is part of the Great Appalachian Valley running from eastern Canada to northern Alabama. This valley is shared by three major watersheds—the Wallkill River, with its tributaries Pochuck Creek and Papakating Creek flowing north; and the Paulins Kill watershed and Pequest River watershed flowing southwest. This valley floor consists of shale and slate (part of the Ordovician Martinsburg Formation) and of limestone (part of the Jacksonburg Formation). Several parties have argued about the possibility of natural gas extraction in the region's Martinsburg and Utica shale formations, similar to the Marcellus Shale formations to the West in Pennsylvania and New York. Of special interest is Rutan Hill, a 440-million-year-old patch of igneous rock known as nepheline syenite. This site, north of Beemerville in Wantage Township, was once an ancient volcano—the only extant dormant volcano site in the state.

Dividing the Kittatinny Valley (and the Ridge and Valley Province) from the Highlands region is a narrow fault of Hardyston Quartzite. Many of the mountains in the Highlands are not part of a solid, linear ridge and tend to randomly rise from the surrounding land as the result of folds, faults and intrusions. Elevations in the Highlands region range from 1,000 to 1,500 feet. The more prominent mountains in this area are Hamburg Mountain (elevation: 1,495 feet (456 m)), Wawayanda Mountain (elevation: 1,448 feet (441 m)), Sparta Mountain (elevation: 1,232 feet (376 m)) and Pochuck Mountain (elevation: 1,194 feet (364 m)) which form a ridge along the county's eastern flank.

Sussex County's rivers and watersheds flow in three directions; north to the Hudson River, west and south to the Delaware River, and east toward Newark Bay.

• Wallkill River is an 88.3-mile-long (142.1 km) river starting at its source at Lake Mohawk in Sparta Township drains north into Rondout Creek, a tributary of the Hudson River. The Wallkill River drains a 785 square miles (2,030 km) watershed.
• Pochuck Creek is an 8.1-mile-long (13.0 km) creek flowing north into the Wallkill River.
• Papakating Creek is a 20.1-mile-long (32.3 km) creek in the north central region of the county beginning in Frankford Township also drains into the Wallkill.
• Clove Creek is a 12.0-mile-long (19.3 km) creek that flows into the Papakating Creek near Lewisburg in Wantage Township.
• The Flat Brook is a 11.6-mile-long (18.7 km) creek flowing through Walpack and Sandyston Townships, joins the Delaware River at the Walpack Bend. It has two main tributaries: the Little Flat Brook whose length is 12.6-mile-long (20.3 km) and Big Flat Brook whose length is 16.5-mile-long (26.6 km).
• The Paulins Kill is a 41.6-mile-long (66.9 km) river with its two branches: the West Branch is fed by Bear Swamp, Lake Owassa, Culver's Lake, and the Dry Brook in Frankford Township, the Main or East Branch starting at Newton combining near Augusta to flow southwest through Hampton, Stillwater, Hardwick, Blairstown, and Knowlton townships to join the Delaware River near the Delaware Water Gap. The Paulins Kill drains a 176.85 square miles (458.0 km) watershed.
• The Pequest River is a 35.7-mile-long (57.5 km) beginning near Newton and Springdale and flowing through in Andover and Green Township, then through Warren County before joining the Delaware near Belvidere.
• The Musconetcong River is a 45.7-mile-long (73.5 km) river beginning at Lake Hopatcong, forms the eastern border between Warren County and Morris and Hunterdon Counties. Its main tributaries are Lubbers Run and Punkhorn Creek.
• Small sections of eastern Sussex County drain into the watersheds of the Pequannock River, Passaic River, and Rockaway River which end in Newark Bay.

Historically, these rivers and streams were used to power various types of mills (i.e. grist mills, fulling mills, etc.), transport goods to market, and later to generate electric power (after 1880). Today, these rivers are chiefly used in local recreational activities—including canoeing and fishing. The Fish Culture Unit of the New Jersey Division of Fish and Wildlife stocks these waterways each year with various species of trout. Some of these rivers—especially the Flat Brook, Paulins Kill and Pequest—have become well known as trout streams and for their suitability for fly-fishing. The Flat Brook and its tributary the Big Flat Brook are regarded as the state's premiere trout stream.

According to the Natural Resource Conservation Service, Sussex County soils are derived from parent materials that are largely till and glaciofluvial deposits, alluvium, and organic matter deposits. Till is the rock of soil material transported or deposited by glacial ice. In this case, the most recent glaciation (i.e. the last ice age), the Wisconsinian continental glacier, deposited a till plain composed of ground and recessional moraines. This glaciation reached its maximum extent roughly 22,000 years ago. Glaciofluvial deposits (or "outwash") are rock and soil materials that melting glaciers deposit as the glacier recedes. Alluvium is materials that are deposited by floodwaters from engorged bodies of water—chiefly streams and rivers. Organic deposits are largely the result of decomposing plant material.

According to the U.S. Census Bureau, as of the 2020 Census, the county had a total area of 535.54 square miles (1,387.0 km), of which 518.66 square miles (1,343.3 km) was land (96.8%) and 16.88 square miles (43.7 km) was water (3.2%). It is the fourth-largest of the state's 21 counties in terms of area.

Sussex County lies within the Kittatinny Mountains of Northwestern New Jersey and the overall Appalachian Mountains range. High Point, located at the northernmost tip of New Jersey in Montague Township, is the highest natural elevation in the state at 1,803 feet (550 m) above sea level. Nearby, Sunrise Mountain in Stokes State Forest has an elevation of 1,653 feet (504 m). Many mountains in the Highlands region range from 1,000 to 1,500 feet (300 to 460 m). Officially, the county's lowest elevation is approximately 300 feet (91 m) above sea level along the Delaware River near Flatbrookville. However, local authorities claim unofficially that the mine adit descending 2,675 feet (815 m) at the Sterling Hill Mine in Ogdensburg is the lowest elevation in New Jersey.

Because of its topography, Sussex County has remained a relatively rural and forested area. In the western half of the county, several state and federal parks have kept the large tracts of land undeveloped and in their natural states. The eastern half of the county has had more suburban development because of its proximity to more populated areas and commercial development zones.

With its location at the top of New Jersey, Sussex County is the only county to neighbor both New York and Pennsylvania. Because it is shaped roughly like a diamond or rhombus with its point matching the cardinal points of the compass, its boundary lines are roughly oriented along the ordinal or intercardinal directions.

Because of its location in the higher elevations of northwestern New Jersey's Appalachian mountains, Sussex County has a cooler humid continental climate or microthermal climate (Köppen Dfb) which indicates patterns of significant precipitation in all seasons and at least four months where the average temperature rises above 10 °C (50 °F) This differs from the rest of the state which is generally a humid mesothermal climate, in which temperatures range between −3 and 18 °C (27 and 64 °F) during the year's coldest month. Sussex County is part of USDA Plant Hardiness Zone 6.

During winter and early spring, New Jersey in some years is subject to "nor'easters"—significant storm systems that have proven capable of causing blizzards or flooding throughout the northeastern United States. Hurricanes and tropical storms, tornadoes, and earthquakes are relatively rare. The Kittatinny Valley to the north of Newton, part of the Great Appalachian Valley, experiences a snowbelt phenomenon and has been categorized as a microclimate region known as the "Sussex County Snow Belt." This region receives approximately forty to fifty inches of snow per year and generally more snowfall that the rest of Northern New Jersey and the Northern Climate Zone. This phenomenon is attributed to the orographic lift of the Kittatinny Ridge which impacts local weather patterns by increasing humidity and precipitation, providing the ski resorts of Vernon Valley in the northeastern part of this region with increased snowfall.

In recent years, average temperatures in the county seat of Newton have ranged from a low of 17 °F (−8 °C) in January to a high of 84 °F (29 °C) in July. Average monthly precipitation ranged from 2.86 inches (73 mm) in February to 4.76 inches (121 mm) in June.

According to the USDA Natural Resource Conservation Service soil survey, the area receives sunshine approximately 62% of the time in summer and 48% in winter. Prevailing winds are typically from the southwest for most of year; but in late winter and early spring come from the northwest. The lowest recorded temperature was −26 °F on January 21, 1994. The highest recorded temperature was 104 °F (40 °C) on September 3, 1953. The heaviest one-day snowfall was 24 inches (610 mm) recorded on January 8, 1996; combined with the next day, total snowfall was 40 inches (1,000 mm). The heaviest one-day rainfall - 6.70 inches (170 mm) was recorded on August 19, 1955.

Historical population

Census	Pop.	Note	%±
1790	19,500		—
1800	22,534		15.6%
1810	25,549		13.4%
1820	32,752		28.2%
1830	20,346	*	−37.9%
1840	21,770		7.0%
1850	22,989		5.6%
1860	23,846		3.7%
1870	23,168		−2.8%
1880	23,539		1.6%
1890	22,259		−5.4%
1900	24,134		8.4%
1910	26,781		11.0%
1920	24,905		−7.0%
1930	27,830		11.7%
1940	29,632		6.5%
1950	34,423		16.2%
1960	49,255		43.1%
1970	77,528		57.4%
1980	116,119		49.8%
1990	130,943		12.8%
2000	144,166		10.1%
2010	149,265		3.5%
2020	144,221		−3.4%
2023 (est.)	146,132		1.3%
Historical sources: 1790–1990 1970–2010 2000 2010 2000–2010 2020 * = Lost territory in previous decade.

This section needs expansion with: examples with reliable citations. You can help by adding to it. (October 2021)

The 2010 United States census counted 149,265 people, 54,752 households, and 40,626 families in the county. The population density was 287.6 per square mile (111.0/km). There were 62,057 housing units at an average density of 119.6 per square mile (46.2/km). The racial makeup was 93.46% (139,504) White, 1.79% (2,677) Black or African American, 0.16% (234) Native American, 1.77% (2,642) Asian, 0.02% (36) Pacific Islander, 1.19% (1,783) from other races, and 1.60% (2,389) from two or more races. Hispanic or Latino of any race were 6.44% (9,617) of the population.

Of the 54,752 households, 33.5% had children under the age of 18; 61% were married couples living together; 9% had a female householder with no husband present and 25.8% were non-families. Of all households, 21% were made up of individuals and 7.4% had someone living alone who was 65 years of age or older. The average household size was 2.69 and the average family size was 3.14.

24% of the population were under the age of 18, 7.6% from 18 to 24, 23.9% from 25 to 44, 32.6% from 45 to 64, and 12% who were 65 years of age or older. The median age was 41.8 years. For every 100 females, the population had 98.5 males. For every 100 females ages 18 and older there were 96.9 males.

As of the 2000 United States census there were 144,166 people, 50,831 households, and 38,784 families residing in the county. The population density was 277 inhabitants per square mile (107/km). There were 56,528 housing units at an average density of 108 units per square mile (42/km). The racial makeup of the county was 95.70% White, 1.0% Black or African American, 0.11% Native American, 1.20% Asian, 0.02% Pacific Islander, 0.74% from other races, and 1.14% from two or more races. 3.30% of the population were Hispanic or Latino of any race. Among those residents listing their ancestry, 24.5% were of Italian, 22.9% German, 22.2% Irish, 10.7% English, 8.1% Polish and 5.2% Dutch ancestry according to Census 2000.

In 2000 there were 50,831 households, out of which 39.9% had children under the age of 18 living with them, 65.0% were married couples living together, 8.0% had a female householder with no husband present, and 23.7% were non-families. 18.9% of all households were made up of individuals, and 6.3% had someone living alone who was 65 years of age or older. The average household size was 2.80 and the average family size was 3.24. In the county, the age distribution of the population shows 27.9% under the age of 18, 6.2% from 18 to 24, 31.5% from 25 to 44, 25.3% from 45 to 64, and 9.1% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 98.0 males. For every 100 females age 18 and over, there were 95.6 males.

Sussex County is considered an affluent area as many of its residents are college-educated, employed in professional or service jobs, and earn above the state's average per capita income and household income statistics. As of 2010, the Bureau of Economic Analysis ranked the county as having the 131st-highest per capita income of all 3,113 counties in the United States (and the ninth-highest in New Jersey). Average per capita income was $49,207 and was 23.2% above the national average.

As of the 2000 Census, the median household income was $65,266 and the median family income was $73,335. Males had a median income of $44,544 compared with $32,487 for females. The per capita income for the county was $26,992. About 6.30% of families and 8.40% of the population were below the poverty line, including 10.50% of those under age 18 and 8.00% of those age 65 or over.

The median value of all homes in Sussex County as of Q4 2021 was $323,687, up 12.1% from the prior year. As of 2010, there were a total of 54,881 households enumerated in the 2010 census, with a reported median household income of $84,115, or mean household income of $96,527. Males had a median income of $50,395 versus $33,750 for females. The per capita income for the county was $26,992. About 2.8% of families and 4.0% of the population were below the poverty line, including 4.1% of those under age 18 and 5.4% of those age 65 or over.

Income and benefits in Sussex County, New Jersey, 2010

Household income	Number of households	Percentage of households
Less than $10,000	1,754	3.2%
$10,000 to $14,999	1,136	2.1%
$15,000 to $24,999	2,771	5.0%
$25,000 to $34,999	4,026	7.3%
$35,000 to $49,999	5,872	10.7%
$50,000 to $74,999	9,365	17.1%
$75,000 to $99,999	8,209	15.0%
$100,000 to $149,999	12,927	23.6%
$150,000 to $199,999	4,714	8.6%
$200,000 or more	4,107	7.5%

As of the 2006–2010 American Community Survey conducted by the U.S. Census Bureau, 3.6% of county residents were living below the poverty line which the government defined as an annual household income under $22,350 for a family of four. However, recent surveys indicate that in the county's town centers, Sussex Borough (15.1%), Newton (12.8%) and Andover Borough (12.7%), poverty levels reach double-digits. Of these poverty-level residents, an estimated 44% are employed, many of them underemployed despite working multiple jobs.

The Bureau of Economic Analysis calculated that the county's gross domestic product was $4.6 billion in 2021, which was ranked 20th in the state and was a 3.9% increase from the prior year.

As of the 2010 Census, the county's unemployment rate was 11.0%. The Census Bureau reported a population of 118,420 persons (above age 16) available for the labor force of which 82,449 (69.6%) were actively employed in civilian labor, and 35,971 (30.4%) were not in the labor force.

Occupations in Sussex County, New Jersey, 2010.

Category	Persons employed	Percentage of labor force
Management, business, science, and arts occupations	29,443	40.1%
Service occupations	11,689	15.9%
Sales and office occupations	18,712	25.5%
Natural resources, construction and maintenance occupations	6,715	9.2%
Production, transportation, and material moving occupations	6,784	9.2%
TOTAL	73,343

Industry in Sussex County, New Jersey, 2010.

Category	Persons employed	Percentage of labor force
Agriculture, forestry, fishing and hunting, and mining	674	0.9%
Construction	5,495	7.5%
Manufacturing	7,922	10.8%
Wholesale trade	2,303	3.1%
Retail trade	8,536	11.6%
Transportation and warehousing, and utilities	3,791	5.2%
Information	2,074	2.8%
Finance and insurance, and real estate and rental and leasing	6,642	9.1%
Professional, scientific, and management, and administrative and waste management services	7,963	10.9%
Educational services, and health care and social assistance	16,268	22.2%
Arts, entertainment, and recreation, and accommodation and food services	6,629	9.0%
Other services, except public administration	2,033	2.8%
Public administration	3,013	4.1%
TOTAL	73,343

Early industry and commerce chiefly centered on agriculture, milling, and iron mining. As iron deposits were exhausted, mining shifted toward zinc deposits near Franklin and Ogdensburg during the late 19th and early 20th centuries. The local economy expanded due to the introduction of railroads and shortly after the Civil War, the town centers hosted factories. However, the factories, railroads and mining declined by the late 1960s. Today, Sussex County features a mix of rural farmland, forests and suburban development. Because agriculture (chiefly dairy farming) has decreased and that the county hosts little industry, Sussex County is considered a "bedroom community" as most residents commute to neighboring counties (Bergen, Essex and Morris counties) or to New York City for work.

Although Sussex County's dairy farming industry has declined significantly in the last 50 years it is still the majority of agricultural production in the region. Trucking has replaced railroads in the transportation of milk products to regional production facilities and markets. Rising taxes, regulation and decreasing profitability in dairy farming have forced farmers to adapt by growing other products or converting their farms to other uses. Many farmers have sold their properties to real estate developers who have built residential housing. Many Sussex County farms are nursery farms producing ornamental trees, plants and flowers used in horticulture, floristry or landscaping. Christmas trees and nursery and greenhouse plants contribute to 51% of the county's annual crop revenues but account for 30% of crop production.

Despite the decline of dairy farming, it is still the largest contributor to the county's annual agricultural revenues. According to the Sussex County Comprehensive Farmland Preservation Plan (2008):

Dairy production has steadily trended downward since 1971, when the county produced 138 million pounds of milk. By 2005 this quantity had fallen to 38.4 million pounds. The decrease is further reflected in the number of dairy farms and milk cows in 1982 as compared to 2002. In 1982 there were 137 dairy farms; by 2002 the number had decreased to only 30. In 1982 there were 6,406 milk cows; in 2002 the quantity had fallen to 1,943.

According to county agricultural statistics, 17.3% of all crop sales ($1.4 million in 2002) were in hay. Nearly 80% of tilled farmland, or 21,195 acres (8,577 ha), on 43% of the farms in the county is dedicated to hay production. Much of hay is grown for feed on livestock farms — especially dairy farms — and never makes it to market and is therefore not included in federal agricultural census data. In 2002, 4,059 acres (1,643 ha) were dedicated to corn cultivation, the majority of it used for feed on the same farms.

According to the 2007 Census of Agriculture compiled by the U.S. Department of Agriculture's National Agricultural Statistics Service, Sussex County has 1,060 farms totaling 65,242 acres (26,403 ha; 101.941 sq mi) out of New Jersey's total 10,327 farms managing 773,450 acres (313,000 ha; 1,208.52 sq mi). This is up from 1,029 farms in the 2002 Census estimate. However, acreage dedicated to agriculture declined by 13.6% from 75,496 acres (30,552 ha; 117.963 sq mi) in 2002. Note though that 102,547 acres—roughly 30% of the county's land area—are under farmland assessment for the purpose of calculating property tax levies. This decrease is total acreage is due, in large part, to "suburban sprawl" as farmers capitalized by converting to commercial and residential development. The average size of a farm in 2007 was 62 acres (25 ha) acres, down from 73 acres (30 ha). The 2007 acreage dedicated to agriculture is roughly 19.6% of the county's land area. The county-wide total agricultural product sales in 2007 was $21,242,000, up from $14,756,000 in 2002. Total county market value of land and buildings in 2007 was $888,955,000, an increase from $520,997,000 in 2002. The average market value per farm was $838,636 (2007), up from $505,823 (2002). This results in a per acre price of $13,625 (2007), up from $7,136 (2002).

With the repeal of several prohibition-era alcohol laws in 1981, 43 wineries have become licensed and are operating in the state. New Jersey wines have grown in stature due to increased marketing and quality, recent successes and awards in competitions, and appreciation by critics. Sussex County is home to three established and operating wineries and three more are in development.

Sussex County's industrial and manufacturing base is no longer towards heavy industry and mining. Today, companies like Thorlabs, are located here.