Perth Amboy is a city in Middlesex County, New Jersey, United States. The City of Perth Amboy is part of the New York metropolitan area. As of the 2010 United States Census, the city's population was 50,814, reflecting an increase of 3,511 (+7.4%) from the 47,303 counted in the 2000 Census, which had in turn increased by 5,336 (+12.7%) from the 41,967 counted in the 1990 Census. Perth Amboy is known as the "City by the Bay," referring to Raritan Bay.