
The area was first settled in 1681, in the vicinity of Bound Brook, and the county was established by charter on May 22, 1688. Somerset County is one of America's oldest counties, and is named after the English county of Somerset.

The county is located in the Central Jersey region and encompasses much of the Raritan Valley. Somerset County was created on May 14, 1688, from portions of Middlesex County.

Somerset County was recently ranked number 3 of 21 NJ counties as one of the healthiest counties in New Jersey, according to an annual report by County Health Rankings and Roadmaps. In 2012, 49.8 percent of Somerset County residents were college graduates, the highest percentage in the state. 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. 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). 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. 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 2), covered the largest total area of any municipality. Somerset County constitutes part of the New York metropolitan area. 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 is a county located in the north-central part of the U.S. Interactive map of Somerset County, New Jersey
