- The Swinomish Indian Reservation is the reservation of the Swinomish Indian Tribal Community, located on Fidalgo Island in western Washington state. The western boundary of the reservation is disputed between the Swinomish Tribe and the United States government. De facto, the reservation is around 15 square miles (39 km2; 9,600 acres) in size. It comprises a substantial portion of the eastern portion of Fidalgo Island. The total reservation population in 2000 was 2,664.