Leigh-on-Sea is a town in southeast Essex, England. Since 1913, it has been administered as part of the Borough of Southend-on-Sea, located three miles to the east, yet has always retained a distinct identity. In 1996, a town council was created, funded by an increased council tax rate in the area.

Leigh-on-Sea was recorded in the Domesday Book of 1086 as Legra. Located next to the sea, Leigh has been primarily a fishing village for most of its history. However, its sheltered position, at the mouth of the Thames gave it some success as a port, with international trade and a shipbuilding business. There is some doubt as to the exact details, but The Mayflower may have been built in Leigh-on-Sea, it certainly was fitted out there.

The arrival of the London, Tilbury and Southend Railway in 1851, spurred develoment of the town, allowing greater trade with London and the rest of the world, and becoming a commuter town where London workers could live.