Castlereagh (/ˈkɑːsəlreɪ/ KAH-səl-ray) was a local government district with the status of borough in Northern Ireland.

[2][3] The borough was divided into four electoral areas: Castlereagh Central, South, East and West.

[4] The last election was due to take place in May 2009, but on 25 April 2008, Shaun Woodward, Secretary of State for Northern Ireland announced that the scheduled 2009 district council elections were to be postponed until the introduction of the eleven new councils in 2011.

[8] The borough was divided between the East Belfast constituency (the wards of Ballyhanwood, Carrowreagh, Cregagh, Downshire, Dundonald, Enler, Gilnahirk, Graham's Bridge, Lisnasharragh, Lower Braniel, Tullycarnet and Upper Braniel), the South Belfast constituency (Beechill, Cairnshill, Carryduff East, Carryduff West, Galwally, Hillfoot, Knockbracken, Minnowburn, Newtownbreda and Wynchurch wards) and the Strangford constituency (Moneyreagh ward) for elections to the Westminster Parliament and Northern Ireland Assembly.

However, this turned out to be unfounded, with the SDLP being the sixth placed runner up, being narrowly beaten by the UUP for the fifth seat.

The area covered by the former Castlereagh Borough Council had a population of 67,272 residents according to the 2011 Northern Ireland census.