Located 1.5 miles due north of the eastern end of Upper Matecumbe Key.

So named on an 1873 survey map drawn by Charles Smith. McGinty Key on U. S. Coast & Geodetic Survey chart #167, "The Elbow To Lower Matecumbe Key" (1919).

Charles M. Brookfield, who was a sounding boat captain for the U.S. Coast & Geodetic Survey during their recharting of the keys in the 1930s, states in an oral history recording: "Originally that was named McGinty Key. When this last Coast Survey party came through, no one knew who McGinty was or how it got its name. So, we decided to rename it for Captain Cotton who was our First Chief of Party for the U.S. Coast & Geodetic Survey." However, as noted above, in 1873 Cotton Key was the name, so it must be coincidence that Brookfield's chief was also named Cotton.