Gilliam County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 1,995, making it the third-least populous county in Oregon. The county seat is Condon. The county was established in 1885 and is named for Cornelius Gilliam, a colonel who commanded the forces of the provisional government of Oregon after the Whitman Massacre.

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.