| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Hermiston | 1 | 20,009 | 19,453 | 0.52% | 2,315 | 9 | City |
| Pendleton | 2 | 17,008 | 17,009 | 0.11% | 1,478 | 12 | City |
| Umatilla | 3 | 8,391 | 7,257 | 2.08% | 1,683 | 5 | City |
| Milton-Freewater | 4 | 7,015 | 7,105 | -0.2% | 3,457 | 2 | City |
| Stanfield | 5 | 2,132 | 2,147 | -0.14% | 1,235 | 2 | City |
| Pilot Rock | 6 | 1,317 | 1,334 | -0.23% | 891 | 1 | City |
| Athena | 7 | 1,185 | 1,194 | -0.17% | 2,158 | 1 | City |
| Weston | 8 | 700 | 709 | -0.28% | 1,304 | 1 | City |
| Echo | 9 | 623 | 635 | -0.32% | 752 | 1 | City |
| Adams | 10 | 385 | 387 | 0% | 1,085 | 0 | City |
| Ukiah | 11 | 229 | 174 | 5.05% | 1,032 | 0 | City |
| Helix | 12 | 194 | 193 | 0% | 1,528 | 0 | City |
Hermiston is the largest city in Umatilla County, with a population of 20,009.
Helix is the smallest city in Umatilla County, with a population of 194.
There are 12 cities in Umatilla County, Oregon.