House Island is a private island in Portland Harbor in Casco Bay, Maine, United States. It is part of the City of Portland. The island is only accessible by boat. Public access is prohibited, except for an on request tour sanctioned by the island's owners. House Island includes three buildings on the east side and Fort Scammell on the west side. The buildings are used as summer residences. The island's name derives from the site of an early European house, believed that built by Capt.