18 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Colby | 1 | 5,566 | 5,623 | -0.2% | 1,520 | 3.66 | City |
| Morgan | 2 | 542 | 558 | -0.73% | 5 | 104.30 | Township |
| West Hale | 3 | 344 | 355 | -0.86% | 6 | 53.94 | Township |
| Brewster | 4 | 284 | 291 | -0.35% | 1,101 | 0.26 | City |
| Smith | 5 | 230 | 240 | -1.29% | 6 | 35.93 | Township |
| South Randall | 6 | 205 | 215 | -1.44% | 2 | 107.42 | Township |
| Rexford | 7 | 195 | 200 | -0.51% | 747 | 0.26 | City |
| Summers | 8 | 157 | 161 | -0.63% | 1 | 144.17 | Township |
| Lacey | 9 | 127 | 131 | -0.78% | 4 | 35.58 | Township |
| Rovohl | 10 | 123 | 127 | -0.81% | 1 | 107.17 | Township |
| East Hale | 11 | 113 | 115 | -0.88% | 2 | 53.90 | Township |
| Levant | 12 | 112 | 49 | 6.67% | 111 | 1.01 | CDP |
| Barrett | 13 | 110 | 114 | -0.9% | 1 | 106.64 | Township |
| Gem | 14 | 94 | 96 | 0% | 281 | 0.33 | City |
| Kingery | 15 | 92 | 93 | 0% | 1 | 143.80 | Township |
| North Randall | 16 | 75 | 76 | 0% | 1 | 53.23 | Township |
| Menlo | 17 | 63 | 66 | -1.56% | 1 | 54.11 | Township |
| Wendell | 18 | 55 | 58 | -1.79% | 1 | 70.85 | Township |
Colby is the largest city in Thomas County, with a population of 5,566.
Wendell is the smallest city in Thomas County, with a population of 55.
There are 18 cities in Thomas County, Kansas.