district, administrative and historic county of Essex, England, bordered on the north by the Crouch estuary and on the south by the Southend-on-Sea urban area on the Thames estuary. The River Roach (formerly Roch) flows through the centre of the district and into the North Sea among the islands, marshes, and mudflats that form the easternmost part of the district. The coast is much used for sailing and recreation, while the inland parts of the district lie within the commuter belt of London. Area 65 square miles (169 square km). Pop. (2001) 78,488.