6 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Union | 1 | 7,705 | 8,144 | -1.13% | 964 | 7.99 | City |
| Monarch Mill | 2 | 1,755 | 1,264 | -0.17% | 313 | 5.61 | CDP |
| Buffalo | 3 | 1,132 | 1,020 | -0.79% | 281 | 4.02 | CDP |
| Jonesville | 4 | 802 | 849 | -1.11% | 790 | 1.01 | Town |
| Lockhart | 5 | 362 | 381 | -1.09% | 1,187 | 0.30 | Town |
| Carlisle | 6 | 312 | 319 | -0.32% | 220 | 1.42 | Town |
Union is the largest city in Union County, with a population of 7,705.
Carlisle is the smallest city in Union County.
There are 6 cities in Union County, South Carolina.