Wasco County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 25,213. Its county seat is The Dalles. The county is named for a local tribe of Native Americans, the Wasco, a Chinook tribe who live on the south side of the Columbia River. It is near the Washington state line. Wasco County comprises The Dalles Micr…Wasco County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 25,213. Its county seat is The Dalles. The county is named for a local tribe of Native Americans, the Wasco, a Chinook tribe who live on the south side of the Columbia River. It is near the Washington state line. Wasco County comprises The Dalles Micropolitan Statistical Area.