| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| El Dorado | 1 | 16,364 | 17,702 | -1.48% | 1,010 | 16 | City |
| Smackover | 2 | 1,573 | 1,627 | -0.69% | 362 | 4 | City |
| Norphlet | 3 | 707 | 759 | -1.39% | 346 | 2 | City |
| Junction City | 4 | 470 | 502 | -1.26% | 414 | 1 | City |
| Huttig | 5 | 421 | 452 | -1.41% | 141 | 3 | City |
| Calion | 6 | 404 | 430 | -1.22% | 377 | 1 | City |
| Strong | 7 | 396 | 417 | -1% | 248 | 2 | City |
| Felsenthal | 8 | 82 | 84 | -1.2% | 56 | 1 | Town |
El Dorado is the largest city in Union County, with a population of 16,364.
Felsenthal is the smallest city in Union County, with a population of 82.
There are 8 cities in Union County, Arkansas.