Skamania County, Washington (Wikipedia) Skamania County (/skəˈmeɪniə/ skə-MAY-nee-ə) is a county located in the U.S. state of Washington. As of the 2020 census, the population was 12,036. The county seat and largest incorporated city is Stevenson, although the Carson River Valley CDP is more populous. Skamania County is included in the Portland-Vancouver-Hillsboro, OR-WA Metropolitan Statistical Area.