Lagoon Island is the northernmost of the Léonie Islands, lying in the entrance to Ryder Bay on the southeast side of Adelaide Island, Antarctica. It was discovered by the French Antarctic Expedition, 1908–10, under Jean-Baptiste Charcot. The island was charted by the British Graham Land Expedition under John Rymill in February 1936 and was so named because with the island on its west side it forms a lagoon.

• List of Antarctic and sub-Antarctic islands

 This article incorporates public domain material from "Lagoon Island". Geographic Names Information System. United States Geological Survey.