Kalgin Island (Dena'ina: Qelghin) is an island in Cook Inlet of the Gulf of Alaska, southwest of the city of Kenai, Alaska, United States. It is part of the Kenai Peninsula Borough and has a land area of 58.722 km2 (22.673 sq mi), is 11.5 km (7.1 mi) long and reported an official resident population of one person as of the 2000 census.