Columbia County, Washington
County seat: Dayton · Population 4,141 (2025) · 869 sq mi
Columbia County is the 38th most populous of Washington's 39 counties, with 4,141 people (2025 estimate). Its county seat is Dayton. The map shows its 2 cities and towns and the 6 neighboring counties.
Columbia County facts
- County seat
- Dayton
- Population (2025 estimate)
- 4,141 +4.7% since 2020
- Land area
- 869 sq mi 31st largest of 39
- Water area
- 5 sq mi
- Population density
- 5 per sq mi
- Established
- 1875
- Same name
- One of 8 Columbia Counties in the US
- Named after
- Columbia River river in North America; flows from British Columbia, through Washington, and along the Washington-Oregon border to the Pacific Ocean
- Largest city
- Dayton 2,538
- Median household income
- $71,810
- Cities and towns
- 2
- ZIP codes
- 5
- Time zone
- Pacific
- FIPS code
- 53013
Cities and towns in Columbia County
Columbia County has 2 incorporated cities, towns and villages. Populations count the people living inside Columbia County; cities that cross a county line also list the other counties.
| Name | Type | Population 2025 | Also in |
|---|---|---|---|
| Dayton (county seat) | City | 2,538 | |
| Starbuck | Town | 143 |
ZIP codes in Columbia County
5 ZIP codes reach into Columbia County. ZIP codes ignore county lines, so some also cover a neighboring county.
- 99328
- 99347 also Garfield and Whitman counties
- 99348 also Walla Walla County
- 99359
- 99361 also Walla Walla County
Population of Columbia County, 2020–2025
Columbia County grew by 185 people (+4.7%) between April 2020 and July 2025: 137 more deaths than births and a net gain of 326 people from migration.
| Year (July 1) | Population |
|---|---|
| 2020 | 3,954 |
| 2021 | 4,021 |
| 2022 | 4,021 |
| 2023 | 4,064 |
| 2024 | 4,046 |
| 2025 | 4,141 |
Neighboring counties
- Garfield County northeast · 2,416 people
- Walla Walla County west · 62,361 people
- Whitman County north · 48,512 people
- Wallowa County, Oregon southeast · 7,595 people
- Umatilla County, Oregon southwest · 81,119 people
- Franklin County west · 102,612 people
Printable Columbia County map
The PDF is a vector file with real text: it prints sharp on Letter paper and you can search it for a town. The PNG is 2400 pixels wide for slides and documents. Both are free to use with a credit to WhichCounty.
- PDF (Letter) (97 KB)
- PNG (2400 px) (79 KB)
Paste this code to embed the map on your site:
Sources
- Boundaries: U.S. Census Bureau, 2025 Cartographic Boundary Files (1:500,000).
- Population: Census Bureau county and city estimates, Vintage 2025. CDP populations: American Community Survey 2020–2024.
- Places and ZIP codes: Census Bureau 2026 Gazetteer and 2020 ZIP Code Tabulation Area relationship files.
- County seat, founding year and name origin: Wikidata (CC0), checked against state sources.
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