26 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Liberty | 1 | 11,146 | 10,919 | 0.16% | 450 | 25 | Township |
| Liberty | 2 | 6,374 | 6,065 | 0.71% | 129 | 49 | Township |
| Liberty | 3 | 4,779 | 4,774 | 0.06% | 152 | 32 | Township |
| Liberty | 4 | 4,520 | 4,424 | 0.47% | 130 | 35 | Township |
| Liberty | 5 | 3,420 | 3,403 | 0% | 80 | 43 | Township |
| Center | 6 | 2,747 | 2,913 | -1.4% | 98 | 28 | Township |
| Liberty | 7 | 2,308 | 2,322 | 0.04% | 66 | 35 | Township |
| Liberty | 8 | 2,238 | 2,207 | 0.4% | 48 | 47 | Township |
| Liberty | 9 | 2,076 | 2,026 | 0.44% | 62 | 33 | Township |
| Liberty | 10 | 1,964 | 1,960 | 0.46% | 91 | 22 | Township |
| Liberty | 11 | 1,950 | 2,043 | -0.76% | 2,478 | 1 | Town |
| Liberty | 12 | 1,771 | 1,764 | 0.57% | 75 | 24 | Township |
| Liberty | 13 | 1,476 | 1,551 | -1.53% | 31 | 47 | Township |
| Liberty | 14 | 1,435 | 1,424 | 0.14% | 35 | 41 | Township |
| Union | 15 | 1,389 | 1,463 | -1.28% | 46 | 30 | Township |
| Liberty | 16 | 1,118 | 1,069 | 0.72% | 31 | 36 | Township |
| Liberty | 17 | 996 | 1,046 | -1.19% | 42 | 24 | Township |
| Liberty | 18 | 897 | 896 | 0.11% | 21 | 42 | Township |
| Liberty | 19 | 872 | 881 | -0.57% | 20 | 44 | Township |
| Brownsville | 20 | 688 | 725 | -1.15% | 24 | 28 | Township |
| Liberty | 21 | 652 | 623 | 0.77% | 17 | 39 | Township |
| West College Corner | 22 | 505 | 526 | -0.59% | 1,891 | 0 | Town |
| Liberty | 23 | 392 | 381 | 0.51% | 23 | 17 | Township |
| Harrison | 24 | 392 | 417 | -1.51% | 13 | 30 | Township |
| Spring Grove | 25 | 331 | 333 | 0% | 1,089 | 0 | Town |
| Whitewater | 26 | 71 | 71 | 0% | 899 | 0 | Town |
Liberty is the largest city in Union County, with a population of 11,146.
Whitewater is the smallest city in Union County, with a population of 71.
There are 26 cities in Union County, Indiana.