Governors Island National Monument is a unit of the United States national park system in New York City. It is located on 22 acres (89,000 m2) of Governors Island, a 172-acre (0.70 km2) island located off the southern tip of Manhattan Island, at the confluence of the Hudson and East rivers in New York Harbor.

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.