| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Longview | 1 | 38,448 | 37,867 | 0.22% | 2,598 | 15 | City |
| Kelso | 2 | 12,795 | 12,726 | -0.05% | 1,573 | 8 | City |
| Woodland | 3 | 6,596 | 6,545 | -0.23% | 1,604 | 4 | City |
| Kalama | 4 | 3,204 | 2,976 | 1.23% | 890 | 4 | City |
| Castle Rock | 5 | 2,439 | 2,448 | -0.12% | 1,164 | 2 | City |
Longview is the largest city in Cowlitz County, with a population of 38,448.
Castle Rock is the smallest city in Cowlitz County, with a population of 2,439.
There are 5 cities in Cowlitz County, Washington.