Fort Jay is a coastal bastion fort and the name of a former United States Army post on Governors Island in New York Harbor, within New York City. Fort Jay is the oldest existing defensive structure on the island, and was named for John Jay, a member of the Federalist Party, New York governor, Chief Justice of the United States, Secretary of State, and one of the Founding Fathers of the United States. It was built in 1794 to defend Upper New York Bay, but has served other purposes. From 1806 to 1904 it was named Fort Columbus, presumably for explorer Christopher Columbus. Today, the National Park Service administers Fort Jay and Castle Williams as the Governors Island National Monument.

Governors Island is a 172-acre (70 ha) island in New York Harbor, within the New York City borough of Manhattan. It is located approximately 800 yards (730 m) south of Manhattan Island, and is separated from Brooklyn to the east by the 400-yard-wide (370 m) Buttermilk Channel. The National Park Service administers a small portion of the north end of the island as the Governors Island National Monument, including two former military fortifications named Fort Jay and Castle Williams. The Trust for Governors Island operates the remaining 150 acres (61 ha), including 52 historic buildings, as a public park. About 103 acres (42 ha) of the land area is fill, added in the early 1900s to the south of the original island.