Somerset County is a county located in the north-central part of the U.S. state of New Jersey. As of the 2020 census, the county was the state's 13th-most-populous county, with a population of 345,361, its highest decennial count ever and an increase of 21,917 (+6.8%) from the 2010 census count of 323,444. Somerset County constitutes part of the New York metropolitan area. Its county seat is Somerville. The most populous place in the county was Franklin Township, with 68,364 residents at the time of the 2020 census, while Hillsborough Township, with 55.00 square miles (142.4 km), covered the largest total area of any municipality. The county is part of the Central Jersey region of the state.
In 2015, Somerset County had a per capita personal income of $86,468, the second highest in New Jersey and ranked 25th of 3,113 counties in the United States. Somerset County, as of the 2000 Census, was the seventh wealthiest county in the United States by median household income at $76,933 (third in New Jersey behind Hunterdon County at $79,888 and Morris County at $77,340), fourth in median family income at $90,655 (second in New Jersey behind Hunterdon County at $91,050) and ranked seventh by per capita income at $37,970 (highest in New Jersey). The Bureau of Economic Analysis ranked the county as having the 11th-highest per capita income of all 3,113 counties in the United States (and the highest in New Jersey) as of 2009. As of 2023, Somerset County had the highest GDP for counties with populations between 100,000 and 500,000 in America.