Dog Key Island was a barrier island on the Gulf Coast of the United States, between Ship Island and Horn Island, and off Biloxi, Mississippi. It has been reported as an island occasionally - in the mid-19th century and the early 20th - while at other times it was submerged. As of 2011 it was a few feet underwater, and NOAA has marked two Nautical passes, "Little Dog Keys" and "Dog Keys", next to it.
As it stood partly off the territorial waters border of the United States, it was at times used for businesses illegal in Mississippi. Bootleggers used the island and its fresh water during prohibition. More famously, in 1926 three partners opened the Isle of Caprice cabanas hotel, a casino resort where alcoholic drink could be sold openly. The place was very popular, but after continued natural erosion and a hurricane that diminished the sandy island, in 1932 it was abandoned. It lends its name to the Isle of Capri Casinos chain, the first of which was set in Biloxi.