The area of the island is 210.4 acres (0.851 km2), its total acreage at low tide is 288, and its highest elevation is 80 feet.
During the American Revolutionary War, more than 600 militiamen were stationed on the island to guard against the return of British troops following their evacuation of Boston by the hand of Gen. George Washington on March 17, 1776.
As of 2008, 26 of the original buildings of Fort Andrews were still standing — guardhouses, prisoner-of-war barracks, stables, a gymnasium, a firehouse, etc.
This will fund a program in which 11 buildings will be demolished and a further 11 restored, in an attempt to make the island more visitor-friendly as a historical museum and nature reserve.
Predominant tree and shrub species on the island include maple, birch, oak, pine, poplar, sumac, and apple.