South Amboy has passed through three of the five types of New Jersey municipalities. It was first mentioned on May 28, 1782, in minutes of the Board of Chosen Freeholders as having been formed from Perth Amboy Township. It was formally incorporated as a township by the Township Act of 1798 on February 21, 1798. Over the next 90 years, portions split off to form Monroe Township (April 9, 1838), Madison Township (March 2, 1869; later renamed as Old Bridge Township) and Sayreville Township (April 6, 1876; later Borough of Sayreville).
South Amboy is a suburban city in Middlesex County, in the U.S. state of New Jersey, located on Raritan Bay. As of the 2020 United States census, the city's population was 9,411, an increase of 780 from the 2010 census count of 8,631, which in turn reflected an increase of 718 from the 7,913 counted in the 2000 census.