 The island is long and covers .Prior to October 2014, access to the island was via a road over a causeway  from the Squantum peninsula of North Quincy to Moon Island, and from there, over a two-lane steel bridge – officially named the Long Island Viaduct – from Moon Island to Long Island.Access to the causeway leading to Moon Island and Long Island is controlled by police at a guardhouse at its southern end, and permission must be obtained in advance since it is a restricted area.