Spokane County is a county located in the U.S. state of Washington. As of the 2020 census, its population was 539,339, making it the fourth-most populous county in Washington. The largest city and county seat is Spokane, the second largest city in the state after Seattle. The county is named after the Spokane tribe.

Kootenai County is located in the U.S. state of Idaho. As of the 2020 census, its population was 171,362, making it the third-most populous county in Idaho and by far the largest in North Idaho, the county accounting for 45.4% of the region's total population. The county seat and largest city is Coeur d'Alene. The county was established in 1864 and named after the Kootenai tribe.