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.

Condon is a city in, and the seat of, Gilliam County, in the U.S. state of Oregon. The population was 682 at the 2010 census. The city, with an historic main street along Oregon Route 19, is a farming and ranching community. The John Day River/Cottonwood Canyon State Park, the ghost town of Lonerock and the John Day Fossil Beds are all a short drive from Historic Condon.