Kupreanof Island is an island in the Alexander Archipelago in southeastern Alaska. The island is long and wide with a total land area is , making it the 13th largest island in the United States and the 170th largest island in the world. The Lindenberg Peninsula, on the southeast side of the island is considered part of the island. The peninsula is separated from the rest of the island by a narrow inlet called Duncan Canal. The island's population was 785 at the 2000 census.