Elections to Castlereagh Borough Council were held on 5 May 2005 on the same day as the other Northern Irish local government elections. The election used four district electoral areas to elect a total of 23 councillors.

Election results

Note: "Votes" are the first preference votes.

Districts summary

|- class="unsortable" align="centre" !rowspan=2 align="left"|Ward ! % !Cllrs ! % !Cllrs ! % !Cllrs ! % !Cllrs ! % !Cllrs !rowspan=2|TotalCllrs |- class="unsortable" align="center" !colspan=2 bgcolor="" | DUP !colspan=2 bgcolor="" | UUP !colspan=2 bgcolor="" | Alliance !colspan=2 bgcolor="" | SDLP !colspan=2 bgcolor="white"| Others |- |align="left"|Castlereagh Central |bgcolor="#D46A4C"|54.4 |bgcolor="#D46A4C"|4 |12.5 |1 |16.3 |1 |6.5 |0 |10.3 |0 |6 |- |align="left"|Castlereagh East |bgcolor="#D46A4C"|59.2 |bgcolor="#D46A4C"|5 |18.9 |1 |12.4 |1 |0.0 |0 |9.5 |0 |7 |- |align="left"|Castlereagh South |bgcolor="#D46A4C"|36.7 |bgcolor="#D46A4C"|2 |18.3 |1 |17.1 |1 |22.2 |0 |5.7 |0 |5 |- |align="left"|Castlereagh West |bgcolor="#D46A4C"|34.1 |bgcolor="#D46A4C"|2 |20.6 |1 |19.9 |1 |20.9 |1 |4.5 |0 |5 |- class="unsortable" class="sortbottom" style="background:#C9C9C9" |align="left"| Total |46.5 |13 |17.8 |4 |16.2 |4 |12.0 |2 |7.5 |0 |23

Districts results

Castlereagh Central

2001: 3 x DUP, 1 x Alliance, 1 x UUP, 1 x PUP 2005: 4 x DUP, 1 x Alliance, 1 x UUP 2001-2005 Change: DUP gain from PUP

Castlereagh East

2001: 4 x DUP, 1 x UUP, 1 x Alliance, 1 x Independent 2005: 5 x DUP, 1 x UUP, 1 x Alliance 2001-2005 Change: DUP gain from Independent

Castlereagh South

2001: 2 x UUP, 1 x DUP, 1 x SDLP, 1 x Alliance 2005: 2 x DUP, 1 x UUP, 1 x SDLP, 1 x Alliance 2001-2005 Change: DUP gain from UUP

Castlereagh West

2001: 2 x DUP, 1 x Alliance, 1 x SDLP, 1 x UUP 2005: 2 x DUP, 1 x Alliance, 1 x SDLP, 1 x UUP 2001-2005 Change: No change

References