South Amboy is a city in Middlesex County, New Jersey, on the Raritan Bay. As of the 2010 United States Census, the city's population was 8,631, reflecting an increase of 718 (+9.1%) from the 7,913 counted in the 2000 Census, which had in turn increased by 50 (+0.6%) from the 7,863 counted in the 1990 Census.