Castlegar is also an ecclesiastical parish in the Roman Catholic Diocese of Galway, Kilmacduagh and Kilfenora.

[2] It extends from Lough Corrib across to Merlin Park by the old Galway-Dublin road.

The eponymous Castlegar Castle, a 15th or 16th century tower house, is historically associated with the Burke (de Burgo) family.

The name Castlegar is derived from the Irish Caisleán Gearr, meaning "short castle".

[5] Castles in the area include:[citation needed] Villages and townlands in the ecclesiastical parish of Castlegar include:[citation needed]