Pepys Island was a phantom island, said to lie about 230 miles north of the Falkland Islands. It was first described by Ambrose Cowley in 1684, presumably mistaking the coordinates of one of the Falkland Islands, and named by him for Samuel Pepys. Other observers on the voyage, such as William Dampier, did not record the island.

Many expeditions attempted to locate the island during the eighteenth century. Some, including John Byron, identified it with the Falkland Islands, but others such as Louis-Antoine de Bougainville, Lord Anson and even Captain Cook continued searching until the 1780s, when Cowley's original journal was rediscovered and his mistake noticed.