Malheur County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 31,571. Its county seat is Vale, and its largest city is Ontario. The county was named after the Malheur River, which runs through the county. The word "malheur" is French for misfortune or tragedy. Malheur County is included in the Ontario, Oregon Micropolitan Statistical Area, which is also included in the Boise Combined Statistical Area. It is included in the eight-county definition of Eastern Oregon.

Baker County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 16,668. The county seat and largest city is Baker City. The county was organized on September 22, 1862, when a portion of Wasco County was partitioned off. The new county's area was reduced in 1864 when Union County was partitioned off, and again in 1887 when Malheur County was partitioned off. The county's lines were last adjusted in 1901 when a parcel was added to the county.