Columbia County, Washington

county in Washington, United States

Columbia County is a county in the U.S. state of Washington. The county seat is Dayton. 3,952 people lived there at the 2020 census[1] which makes it the third-least populous county in Washington. The county was created out of Walla Walla County on November 11, 1875[2] and is named after the Columbia River.

Columbia County
Columbia County Courthouse in Dayton
Columbia County Courthouse in Dayton
Map of Washington highlighting Columbia County
Location within the U.S. state of Washington
Map of the United States highlighting Washington
Washington's location within the U.S.
Coordinates: 46°18′N 117°55′W / 46.3°N 117.92°W / 46.3; -117.92
Country United States
State Washington
FoundedNovember 11, 1875
Named forColumbia River
Largest cityDayton
 • Total873 sq mi (2,260 km2)
 • Land869 sq mi (2,250 km2)
 • Water4.9 sq mi (13 km2)  0.6%
 • Total3,952
 • Density4.6/sq mi (1.8/km2)
Time zoneUTC−8 (Pacific)
 • Summer (DST)UTC−7 (PDT)
Congressional district5th


  1. "QuickFacts: Columbia County, Washington". United States Census Bureau. Retrieved January 20, 2024.