Foulness Island is a closed island on the east coast of Essex in England, which is separated from the mainland by narrow creeks. In the 2001 census, the usually resident population of the civil parish was 212, living in the settlements of Churchend and Courtsend, at the north end of the island. The population reduced to 151 at the 2011 Census. The island had until recently a general store and post office. The George and Dragon pub in Churchend closed in 2007, while the church of St Mary the Virgin closed in May 2010. In 2019, the Southend Echo reported plans for the church to be converted into a five-bedroom home.

A closed city or town is a settlement where travel or residency restrictions are applied so that specific authorization is required to visit or remain overnight. Such places may be sensitive military establishments or secret research installations that require much more space or internal freedom than is available in a conventional military base. There may also be a wider variety of permanent residents, including close family members of workers or trusted traders who are not directly connected with clandestine purposes.