Fat Deer Key is an island in the Middle Keys of Florida. The Overseas Highway (U.S. 1) crosses the key at approximately mile markers 53.5-56, between Long Point Key and Key Vaca. It is entirely within the cities of Marathon, Florida and Key Colony Beach, Florida. It has the only road leading to the city of Key Colony Beach, known as Sadowski Causeway.
The 1873 Charles Smith Survey map shows Fat Deer Keys. A.D. Bache, in the notes for his Coast Survey conducted in 1861, reported the remains of a settlement on this key and so named it. Formerly known as Bonefish Key. Fat Deer Key is one of Marathon Florida’s many neighbourhoods travellers like to visit.