Castle Island, Boston: Peninsula, Not Island — History & Access

Castle Island is not an island. It's a peninsula in South Boston, connected to the mainland by a narrow causeway and two bridges — but its name persists from when it was an island.

Geographic Reality

• Location: South Boston, jutting into Boston Harbor (Dorchester Bay)
• Connection: Day Boulevard causeway + two vehicle/pedestrian bridges
• Size: 22 acres (8.9 ha)
• Elevation: ~10 ft — low, exposed

Historical Evolution

• Pre-colonial: Tidal island used by Massachusett people.
• 1634: Fort Independence (first fortification) — "Castle William" to British.
• 1776: British evacuate; Americans occupy.
• 1800s: Rebuilt as pentagonal granite fort (current Fort Independence, 1834–1851).
• 1890s: Landfill connects to mainland (South Boston expansion).
• 1962: Transferred to Massachusetts; now state park.

Today: Recreation & History

• Fort Independence: Free tours (seasonal); National Register of Historic Places.
• Pleasure Bay Beach: Popular swimming (lifeguards summer).
• Loop trail: 1.1 mi paved — walking, running, biking, Harborwalk connection.
• Sullivan's: Iconic seafood shack (fried clams, hot dogs) since 1950s.
• Events: July 4th fireworks viewing, festivals.

Access

• Car: Day Blvd from I-93 (Exit 15) — limited parking (fills summer weekends).
• Transit: Red Line to JFK/UMass → Bus #11 (or 20-min walk).
• Bike: Harborwalk from downtown (3 mi).

Why the Name Stuck

"Castle Island" survived 130 years of peninsula status because the fort's identity dominated. It's a place-name fossil — like "Coney Island" (peninsula since 1920s) or "Marblehead Neck" (tombolo).