8 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| La Grande | 1 | 13,071 | 13,006 | 0.1% | 2,852 | 5 | City |
| Union | 2 | 2,116 | 2,151 | -0.33% | 850 | 2 | City |
| Elgin | 3 | 1,689 | 1,714 | -0.3% | 1,671 | 1 | City |
| Island City | 4 | 1,127 | 1,145 | -0.35% | 1,145 | 1 | City |
| Cove | 5 | 615 | 625 | -0.32% | 765 | 1 | City |
| North Powder | 6 | 497 | 502 | -0.2% | 791 | 1 | City |
| Imbler | 7 | 241 | 246 | -0.41% | 1,116 | 0 | City |
| Summerville | 8 | 121 | 120 | 0% | 458 | 0 | Town |
La Grande is the largest city in Union County, with a population of 13,071.
Summerville is the smallest city in Union County, with a population of 121.
There are 8 cities in Union County, Oregon.