Somerset County is located in the U.S. state of New Jersey. It is part of the New Jersey Metropolitan Area. Somerset County ranks 7th among the highest-income counties in the United States with a per capita income of $37,970. Somerset County is one of America's oldest counties.Somerset County has a total area of approximately 305 square miles of which 99.9% is land and 0.1% water. As of the 2000 census, there were 297,490 people, 108,984 households, and 78,359 families residing in Somerset County, NJ.