15 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Longview | 1 | 38,400 | 37,819 | 0.28% | 2,595 | 15 | City |
| Longview | 2 | 38,400 | 37,869 | 0.28% | 2,595 | 15 | City |
| Kelso | 3 | 12,738 | 12,716 | 0.01% | 1,566 | 8 | City |
| Kelso | 4 | 12,738 | 12,732 | 0.01% | 1,566 | 8 | City |
| Woodland | 5 | 6,483 | 6,529 | -0.2% | 1,577 | 4 | City |
| Woodland | 6 | 6,483 | 6,547 | -0.2% | 1,577 | 4 | City |
| Lexington | 7 | 5,686 | 3,785 | 7.14% | 4,246 | 1 | CDP |
| Longview Heights | 8 | 4,286 | 4,388 | 0.68% | 1,030 | 4 | CDP |
| Kalama | 9 | 3,170 | 2,959 | 1.25% | 880 | 4 | City |
| Kalama | 10 | 3,170 | 2,973 | 1.25% | 880 | 4 | City |
| Beacon Hill | 11 | 2,653 | 1,903 | 7.15% | 2,309 | 1 | CDP |
| Castle Rock | 12 | 2,443 | 2,449 | -0.08% | 1,166 | 2 | City |
| Castle Rock | 13 | 2,443 | 2,451 | -0.08% | 1,166 | 2 | City |
| Ryderwood | 14 | 432 | 401 | 0.47% | 2,683 | 0 | CDP |
| Cougar | 15 | 41 | 93 | 7.89% | 71 | 1 | CDP |
Longview is the largest city in Cowlitz County, with a population of 38,400.
Cougar is the smallest city in Cowlitz County, with a population of 41.
There are 15 cities in Cowlitz County, Washington.