The Town of Winthrop is a city in Suffolk County, Massachusetts, United States. The population was 17,497 at the 2010 census. Winthrop is an ocean-side suburban community in Greater Boston situated at the north entrance to Boston Harbor, close to Logan International Airport. It is located on a peninsula, 1.6 square miles (4.2 km2) in area, connected to Revere by a narrow isthmus and to East Boston by a bridge over the harbor inlet to the Belle Isle Marsh Reservation.