Fort Jefferson is a former U.S. military coastal fortress in the Dry Tortugas National Park of Florida. It is the largest brick masonry structure in the Americas, covering 16 acres and made with over 16 million bricks. Among United States forts, only Fort Monroe in Virginia and Fort Adams in Rhode Island are larger. The fort is located on Garden Key in the lower Florida Keys within the Dry Tortugas, 68 miles west of the island of Key West. The Dry Tortugas are part of Monroe County in Florida.