Washington's 4th congressional district encompasses a large area of central Washington, covering the counties of Douglas, Okanogan, Grant, Yakima, Benton, and Klickitat; and parts of Adams and Franklin counties. The district is dominated by the Yakima and Tri-Cities areas. With a Cook Partisan Voting Index rating of R+11, it is the most Republican district in Washington.

Douglas County is a county located in the U.S. state of Washington. As of the 2020 census, its population was 42,938. The county seat is Waterville, while its largest settlement is East Wenatchee. The county was created out of Lincoln County on November 28, 1883 and is named for American statesman Stephen A. Douglas.