Green Island, also known as North Brewster Island, is a rocky outer island in the Boston Harbor Islands National Recreation Area, to the north of Calf Island and Hypocrite Channel. The island has a permanent size of 2.5 acres (10,000 m2), plus an intertidal zone of a further 15 acres (61,000 m2), and is exposed from the east and northeast with little soil or plant life. The island is named after , a well-known merchant, who owned the island during Colonial times.