Located between Sand Key and the Eastern Dry Rocks.

So named on U.S. Coast Survey Chart of 1855. The U.S. Coast & Geodetic Survey Chart #169 (1878) shows a dry key named Rock Key on the reef midway between Sand Key and the Eastern Dry Rocks. It is also shown on current charts.

F.W. Gerdes, in his journal for the years 1848-49 states: "Rock Key is an island containing perhaps 3 or 4 acres of sandy surface, mixed with small rocky substances; it exists only since a year or two." Gerdes states at another point that Rock Key was formed by the 1846 hurricane.