Hat Island, also known as Gedney Island, is a small island in Possession Sound in the U.S. state of Washington. The island is covered by a census-designated place (CDP) that is part of Snohomish County. The population is 26 as of 2025. The island lies between the mainland city of Everett, Washington, and the southern part of Whidbey Island; it has a land area of 1.768 km2 (436.8 acres).