Southgate, city, Wayne County, southeastern Michigan, near the city of Detroit and the Detroit River; separated from Ecorse Township and incorporated 1958. It is a residential community with commercial activity. Southgate has some industry, including the manufacture of motor-vehicle parts. The community, settled in the late 18th century, is named for its function as a gateway to Detroit from the south. Population 32,058 (1980); 30,771 (1990); 30,136 (2000).