Castle Island may refer to:
Bermuda Castle Island, Bermuda, one of the islands of Castle Harbour, Bermuda Castle Islands Fortifications, Bermuda
Canada Castle Island, Alberta Castle Island, Manitounuk Islands, Nunavut
Greenland Castle Island (Greenland), an island in Sherard Osborn Fjord
Ireland Castle Island (County Cork), and uninhabited island in Roaringwater Bay (51.507518N, 9.504267W) Castle Island (County Roscommon), an island in Lough Key Castleisland, a town in County Kerry, Ireland
New Zealand Castle Island, New Zealand
United Kingdom Castle Island, County Down, a townland in County Down, Northern Ireland Castle Island, County Antrim, a townland in County Antrim, Northern Ireland Castle Island, England, an ait of the River Wansbeck, Northumberland Castle Island, Scotland
United States Castle Island (Massachusetts), a peninsula in Boston Harbor Castle Island (New York), formerly an island in the Hudson River currently part of the Port of Albany-Rensselaer in Albany, New York Castle Island (Washington), one of the San Juan Islands