The City of Colchester is a local government district and borough, with city status, in Essex, England, named after its main settlement, Colchester. The borough covers an area of 125 square miles (320 km2) and stretches from Dedham Vale on the Suffolk border in the north to Mersea Island on the Colne Estuary in the south. The borough was formed on 1 April 1974 by the merger of the former borough of Colchester, covering an area of around 17.7 square miles (46 km2), with the urban districts of West Mersea and Wivenhoe, along with Rural District.