12 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Hermiston | 1 | 19,888 | 19,461 | 0.36% | 2,301 | 9 | City |
| Pendleton | 2 | 17,035 | 17,007 | 0.03% | 1,480 | 12 | City |
| Umatilla | 3 | 8,219 | 7,259 | 1.99% | 1,648 | 5 | City |
| Milton-Freewater | 4 | 6,963 | 7,106 | -0.34% | 3,432 | 2 | City |
| Stanfield | 5 | 2,104 | 2,145 | -0.33% | 1,218 | 2 | City |
| Pilot Rock | 6 | 1,302 | 1,334 | -0.38% | 881 | 1 | City |
| Athena | 7 | 1,177 | 1,197 | -0.25% | 2,144 | 1 | City |
| Weston | 8 | 700 | 715 | -0.28% | 1,304 | 1 | City |
| Echo | 9 | 622 | 636 | -0.32% | 751 | 1 | City |
| Adams | 10 | 388 | 390 | 0% | 1,093 | 0 | City |
| Ukiah | 11 | 248 | 173 | 5.53% | 1,117 | 0 | City |
| Helix | 12 | 191 | 193 | 0% | 1,504 | 0 | City |
Hermiston is the largest city in Umatilla County, with a population of 19,888.
Helix is the smallest city in Umatilla County, with a population of 191.
There are 12 cities in Umatilla County, Oregon.