Plainsboro Township is a township situated in southern Middlesex County, in the U.S. state of New Jersey. Centrally located in the Raritan Valley region, the township is an outer-ring suburb of New York City in the New York metropolitan area, even though it is slightly geographically closer to Center City, Philadelphia than to Midtown Manhattan. As of the 2020 United States census, the township's population was 24,084, its highest decennial count ever and an increase of 1,085 (+4.7%) from the 22,999 recorded at the 2010 census, which in turn reflected an increase of 2,784 (+13.8%) from the 20,215 counted in the 2000 census.