Sunbury-on-Thames, also known as Sunbury, is a town in the Surrey borough of Spelthorne, England, and part of the London commuter belt. It is located 16 miles (25 km) southwest of central London and bordered by Feltham and Hampton, flanked on the south by the River Thames.
Sunbury-on-Thames is historically in Middlesex, forming the Sunbury-on-Thames Urban District from 1894. In 1965, most of Middlesex was absorbed into Greater London. However, the Sunbury-on-Thames Urban District was instead transferred to Surrey. The Royal Mail did not adopt the change in 1965 and the postal county remained Middlesex; although postal counties are no longer officially in use. In 1974 the urban district was abolished and it has since formed part of the borough of Spelthorne.