In 1883, Lincoln County was created from a portion of Spokane County, and four days later it, in turn, lost territory in the creation of Douglas County. Since that time there have been no changes in the boundaries of Lincoln County.
The Swinomish Reservation is roughly 15 square miles (39 km2; 9,600 acres) in size, 7,450 acres (3,010 ha) of which are upland and 2,900 acres (1,200 ha) of which are tidelands.