Somerville is a borough in Somerset County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 12,098, reflecting a decline of 325 from the 12,423 counted in the 2000 Census, which had in turn increased by 791 from the 11,632 counted in the 1990 Census. It is the county seat of Somerset County.Somerville was originally formed as a town on March 25, 1863, within a portion of Bridgewater Township. Somerville was incorporated as a borough by an act of the New Jersey Legislature on April 16, 1909, based on the results of a referendum held on May 4, 1909, at which point it was fully set off from Bridgewater Township.The borough is named for Somerset in England.