Chart of average one-bedroom by county. Data are based on one-bedroom rental units and were collected in September (end of Q3) of each year reported. All data points increased each year, with the steepest average increase from 2019 to 2020. From most expensive to least expensive (in 2021) the listed counties are: King, Clark, Skagit, Thurston, Whatcom, Benton/Franklin, Spokane, Walla Walla, Cowlitz, Kittitas, and Whitman. Source is Washington Center for Real Estate Research at UW.