Castlereagh
- Castlerea
- Castlereagh (County Down barony)
- Castlereagh (County Down townland)
- Castlereagh (County Roscommon barony)
- Castlereagh (borough)
- Castlereagh Highway
- Castlereagh Lower
- Castlereagh River
- Castlereagh Street
- Castlereagh Upper
- Castlereagh, New South Wales
- Castlereagh, Nova Scotia
- Castlereigh Dam
- List of townlands of County Offaly
- List of townlands of County Roscommon
- List of townlands of County Waterford
- Marquess of Londonderry
- Nuwara Eliya
- Robert Stewart, Viscount Castlereagh
- The Castlereagh (Gilgandra)