Columbia County, Washington
Columbia County Courthouse in Dayton
Location within the U.S. state of Washington
Washington's location within the U.S.
|Founded||November 11, 1875|
|Named for||Columbia River|
|• Total||873 sq mi (2,260 km2)|
|• Land||869 sq mi (2,250 km2)|
|• Water||4.9 sq mi (13 km2) 0.6%%|
| • Estimate |
|• Density||4.6/sq mi (1.8/km2)|
|Time zone||UTC−8 (Pacific)|
|• Summer (DST)||UTC−7 (PDT)|
Columbia County is a county in the U.S. state of Washington. The county seat is Dayton. 4,078 people lived there at the 2010 census which makes it the third-smallest populous county in Washington. The county was created out of Walla Walla County on November 11, 1875 and is named after the Columbia River.