South Brunswick is a township in Middlesex County, in the U.S. state of New Jersey. The township is centrally located within the Raritan Valley region and is an outer-ring suburb of New York City in the New York metropolitan area. As of the 2020 United States census, the township's population was 47,043, its highest ever decennial census count and …South Brunswick is a township in Middlesex County, in the U.S. state of New Jersey. The township is centrally located within the Raritan Valley region and is an outer-ring suburb of New York City in the New York metropolitan area. As of the 2020 United States census, the township's population was 47,043, its highest ever decennial census count and an increase of 3,626 from the 2010 census count of 43,417, which in turn reflected an increase of 5,683 from the 37,734 counted in the 2000 census.