seaport and unitary authority, geographic and historic county of Essex, England, lying on the north bank of the Thames estuary. Its southern part was largely reclaimed from the Thames marshes by immigrant Dutch workers. Thurrock's chief town and administrative centre, Grays, was originally a fishing village but eventually became a river port for London's hay and grain market. At West Tilbury, Elizabeth I made her well-known speech to her troops in 1588 at the time of the threatened invasion by the Spanish Armada. The nearby Tilbury Docks were built (1884–86) on what had been uninhabited marsh. Thurrock's industries now stretch along the Thames and include soap and margarine works, cement works, and timber yards. The unitary authority includes rural sections as well as several suburban towns. At its eastern end are huge oil refineries at Shell Haven and Coryton. Area 63 square miles (163 square km). Pop. (2005 est.) 146,600.