Cudjoe Key is a census-designated place in Monroe County, Florida, on an island of the same name in the lower Florida Keys. As of the 2000 census, the CDP had a total population of 1,695. It was originally called Littleton Island.

It has a U.S. Army missile tracking station built during the Cuban missile crisis in 1960. The station flies a white radar aerostat, known locally as "Fat Albert," that runs a drug interdiction mission for the Drug Enforcement Administration. On April 20, 2007 a Cessna 182 crashed after its left wing struck the tether anchoring "Fat Albert" . The aerostat is marked on air navigation charts inside a restricted area that contains the warning, "Caution: Unmarked balloon on cable to 14,000 [feet]."

Possibly named for the Joewood tree (Jacquinia keyensis Mez), a native species which is also known as cudjoewood. A more likely derivation for the name is offered by writer John Viele of Summerland Key. He believes that Cudjoe, a very common West African name, was the name of a runaway or freed black who lived on the island at some point prior to Gerdes' survey in 1849.