12 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Hermiston | 1 | 19,817 | 19,461 | 0.36% | 2,293 | 9 | City |
| Pendleton | 2 | 17,030 | 17,007 | 0.02% | 1,480 | 12 | City |
| Umatilla | 3 | 8,059 | 7,259 | 2.03% | 1,616 | 5 | City |
| Milton-Freewater | 4 | 6,987 | 7,106 | -0.34% | 3,444 | 2 | City |
| Stanfield | 5 | 2,111 | 2,145 | -0.33% | 1,222 | 2 | City |
| Pilot Rock | 6 | 1,307 | 1,334 | -0.46% | 884 | 1 | City |
| Athena | 7 | 1,180 | 1,197 | -0.34% | 2,149 | 1 | City |
| Weston | 8 | 702 | 715 | -0.43% | 1,307 | 1 | City |
| Echo | 9 | 624 | 636 | -0.48% | 754 | 1 | City |
| Adams | 10 | 388 | 390 | -0.26% | 1,093 | 0 | City |
| Ukiah | 11 | 235 | 173 | 5.38% | 1,059 | 0 | City |
| Helix | 12 | 191 | 193 | -0.52% | 1,504 | 0 | City |
Hermiston is the largest city in Umatilla County, with a population of 19,817.
Helix is the smallest city in Umatilla County, with a population of 191.
There are 12 cities in Umatilla County, Oregon.