| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Ellensburg | 1 | 21,144 | 21,651 | -0.77% | 2,394 | 9 | City |
| Union Gap | 2 | 6,629 | 6,588 | 0.18% | 1,189 | 6 | City |
| Cle Elum | 3 | 2,311 | 2,174 | 1.01% | 514 | 4 | City |
| Kittitas | 4 | 1,436 | 1,453 | -0.28% | 1,839 | 1 | City |
| Roslyn | 5 | 961 | 963 | -0.1% | 219 | 4 | City |
| South Cle Elum | 6 | 590 | 564 | 0.34% | 1,468 | 0 | Town |
Ellensburg is the largest city in Kittitas County, with a population of 21,144.
South Cle Elum is the smallest city in Kittitas County, with a population of 590.
There are 6 cities in Kittitas County, Washington.