North Plainfield is a borough in Somerset County, in the U.S. state of New Jersey. It is located within the Raritan Valley region. As of the 2020 United States census, the borough's population was 22,808, an increase of 872 from the 2010 census count of 21,936, which in turn reflected an increase of 833 from the 21,103 counted in the 2000 census. North Plainfield Township was created from portions of Warren Township by an act of the New Jersey Legislature passed on April 2, 1872.