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 was 41 at the 2010 census. 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.

The Snohomish people are a Lushootseed-speaking Southern Coast Salish people who are indigenous to the Puget Sound region of Washington State. Most Snohomish are enrolled in the Tulalip Tribes of Washington and reside on the reservation or nearby, although others are enrolled in other tribes, and some are members of the non-recognized Snohomish Tribe of Indians. Traditionally, the Snohomish occupied a wide area of land, including the Snohomish River, parts of Whidbey and Camano Islands, and the nearby coastline of Skagit Bay and Puget Sound. They had at least 25 permanent villages throughout their lands, but in 1855, signed the Treaty of Point Elliott and were relocated to the Tulalip Reservation. Although some moved to the reservation, the harsh conditions, lack of land, and oppressive policies of the United States government caused many to leave.