Great Diamond, home to Fort McKinley, is just northeast of its neighbor Little Diamond Island, linked only by a sandbar at low tide. The island has a limited network of roads, used primarily by golf carts and bicycles. Access is by about a half hour ferry ride from Portland Harbor, with two landing sites. Landing site at Diamond Cove in the north end is suspended in winter.
The island is the site of historic Fort McKinley with its wide parade ground and its adjacent fine brick homes, once used as officers’ quarters, but now privately owned. Visitors are expected to keep to the main road, Diamond Avenue, since most other roads are private.