8 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| La Grande | 1 | 13,084 | 13,006 | 0.1% | 2,855 | 5 | City |
| Union | 2 | 2,109 | 2,151 | -0.33% | 847 | 2 | City |
| Elgin | 3 | 1,684 | 1,714 | -0.3% | 1,666 | 1 | City |
| Island City | 4 | 1,124 | 1,145 | -0.27% | 1,142 | 1 | City |
| Cove | 5 | 613 | 625 | -0.33% | 762 | 1 | City |
| North Powder | 6 | 496 | 502 | -0.2% | 790 | 1 | City |
| Imbler | 7 | 240 | 246 | -0.41% | 1,111 | 0 | City |
| Summerville | 8 | 121 | 120 | 0% | 458 | 0 | Town |
La Grande is the largest city in Union County, with a population of 13,084.
Summerville is the smallest city in Union County, with a population of 121.
There are 8 cities in Union County, Oregon.