Dry Tortugas National Park, national park located on the Dry Tortugas islands, southwestern Florida, U.S. The islands are situated at the entrance to the Gulf of Mexico, west of Key West, Fla. Established in 1935 as Fort Jefferson National Monument, the park occupies an area of about 101 square miles (262 square km). Its current name was adopted in 1992. The park’s principal features are a marine exhibit and the remains of fortifications built in 1846.