Moon Island is situated in Quincy Bay, in the middle of Boston Harbor, Massachusetts, and is the location of the Boston Fire Department Training Academy, and Boston Police Department shooting range. All of the land on the island is owned by the City of Boston but the island is under the jurisdiction of Quincy, Massachusetts. It is also part of the Boston Harbor Islands National Recreation Area.
The causeway to Moon Island did not exist before the late 1870s and there was no bridge across Western Way to Long Island until the construction of the Long Island Viaduct in 1951. This bridge was closed October 8, 2014. The sand spit from Thompson Island to Squaw Rock on Squantum was a clam bar until the sewage outflow from Moon Island backed up into the local waters. Native Americans summered in this area for thousands of years and consumed the prevalent mollusks.
Another two bars pointed from Moon Island toward Squantum, following the general path of the new causeway. In early years, the land where UMass Boston and the Kennedy Memorial are located was open water. The area around Marina Bay was salt marsh leaving a much wider mouth to the Neponset River.
In Colonial times, Moon Island was recorded as having 20 acres (81,000 m2) of land mass that was used as pasture. This land was connected at very low tides by two sand bars. The proper approach to this island in the late 19th century was from the Quincy Bay side. There was a 100-foot (30 m) hill on the northerly side. Early inhabitants called the island, "Munning's Moone," or "Mennen's Moon," and is also recorded as "Moon Island" and "Moon Head".