Fort Jefferson is a massive but unfinished coastal fortress. It is the largest brick masonry structure in the Americas,and is composed of 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 National Park, about 70 miles (110 km) west of the island of Key West. The Dry Tortugas are part of Monroe County, Florida, United States.
A series of engineering studies and bureaucratic delays consumed the next 17 years, but the construction of Fort Jefferson (named after the third President, Thomas Jefferson) was finally begun on Garden Key in 1846.