8 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| La Grande | 1 | 12,952 | 13,004 | -0.08% | 2,826 | 4.58 | City |
| Union | 2 | 2,096 | 2,150 | -0.52% | 842 | 2.49 | City |
| Elgin | 3 | 1,677 | 1,714 | -0.42% | 1,659 | 1.01 | City |
| Island City | 4 | 1,107 | 1,141 | -0.63% | 1,125 | 0.98 | City |
| Cove | 5 | 613 | 625 | -0.33% | 762 | 0.80 | City |
| North Powder | 6 | 490 | 504 | -0.61% | 780 | 0.63 | City |
| Imbler | 7 | 241 | 246 | -0.41% | 1,116 | 0.22 | City |
| Summerville | 8 | 115 | 119 | -0.86% | 436 | 0.26 | Town |
La Grande is the largest city in Union County, with a population of 12,952.
Summerville is the smallest city in Union County.
There are 8 cities in Union County, Oregon.