Dayton
- County:
- Columbia County
- County Seat:
- Yes
- Area (mi²):
- 1.442
- State:
- Washington
Dayton is a city located in Columbia County, Washington. Dayton has a 2026 population of 2,471. It is also the county seat of Columbia County. Dayton is currently declining at a rate of -0.88% annually but its population has increased by 0.94% since the most recent census, which recorded a population of 2,448 in 2020.