Kelso
- County:
- Cowlitz County
- County Seat:
- Yes
- Area (mi²):
- 8.135
- State:
- Washington
Kelso is a city located in Cowlitz County, Washington. Kelso has a 2026 population of 12,737. It is also the county seat of Cowlitz County. Kelso is currently growing at a rate of 0.7% annually and its population has increased by 0.04% since the most recent census, which recorded a population of 12,732 in 2020.