Somerset County area

Population and density of Somerset County

The Census Bureau estimates that 356,486 people lived in Somerset County on July 1, 2025. That ranks #213 of 3,222 county equivalents nationally and #13 of 21 in New Jersey. Since the April 1, 2020 estimates base of 345,349, the population has grown by 11,137 (+3.2%), compared with +2.8% for New Jersey as a whole.

With 301.9 square miles of land, that is 1,181 people per square mile (456 per km²), placing Somerset County #153 nationally for density and #10 in New Jersey. The median county equivalent has 47 people per square mile; the New Jersey median is 1,137. Put another way, there are about 0.542 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in Somerset County

Somerset County is divided into 21 municipalities and townships. In New Jersey, county subdivisions are local governments, and together they cover all of the county’s land and residents.

The most populous is Franklin township, with 69,105 residents (19.4% of the county). The largest by land is Hillsborough township, at 54.6 mi², or 18.1% of the county’s land. The county seat, Somerville borough, has 14,665 residents. Among those with at least 1,000 residents in 2020, Somerville borough grew fastest since then (+18.8%).

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each subdivision inside Somerset County. Land: 2026 Census Gazetteer. How communities are listed.

Metropolitan area

Somerset County is a central county of the New York-Newark-Jersey City, NY-NJ Metropolitan Statistical Area, in the Lakewood-New Brunswick, NJ metropolitan division. Its 22 county equivalents have 20,112,448 residents on 6,139.7 square miles of land; Somerset County accounts for 4.9% of the land and 1.8% of the residents. By combined land it ranks #34 of 393 metropolitan areas, and #1 by population. It belongs to the New York-Newark, NY-NJ-CT-PA Combined Statistical Area.

ZIP codes

33 ZIP Code Tabulation Areas have land in Somerset County; 27 of them have most of their land inside the county, and the others mainly cover neighboring areas.

070590706007062070630706907920079210792407931079340793907977079790850208525085280854008553085580880508807088120882108823088350883608844088530886908873088760888008890

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Somerset County

Somerset County shares a land border with 5 county equivalents. It has more land than 2 of them. The largest neighbor is Morris County (461 mi²) and the smallest is Union County (102.8 mi²). Together with its neighbors, Somerset County forms a block of 1,827.3 mi² of land, of which it holds 16.5%.

How big is Somerset County compared with U.S. states?

Somerset County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 3.4 times as much. New Jersey’s county land could hold about 24 areas the size of Somerset County.

Another way to picture it: the same land area would fill a square about 17.4 miles (28 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about Somerset County?

Somerset County has more land than 414 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places Somerset County at #2,839 nationally by total area, 31 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.

Its water share is 1%, compared with a national county-equivalent median of 1.2% — 0.2 percentage points lower. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside Somerset County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.