17 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Colby | 1 | 5,504 | 5,609 | -0.31% | 1,503 | 4 | City |
| Morgan | 2 | 529 | 560 | -1.31% | 5 | 104 | Township |
| West Hale | 3 | 340 | 353 | -0.58% | 6 | 54 | Township |
| Brewster | 4 | 278 | 290 | -0.71% | 1,078 | 0 | City |
| Smith | 5 | 237 | 244 | -0.42% | 7 | 36 | Township |
| South Randall | 6 | 204 | 215 | -0.97% | 2 | 107 | Township |
| Rexford | 7 | 195 | 201 | -0.51% | 747 | 0 | City |
| Summers | 8 | 164 | 172 | -0.61% | 1 | 144 | Township |
| Lacey | 9 | 124 | 129 | -0.8% | 3 | 36 | Township |
| Rovohl | 10 | 121 | 126 | -0.82% | 1 | 107 | Township |
| East Hale | 11 | 114 | 117 | -0.87% | 2 | 54 | Township |
| Barrett | 12 | 111 | 116 | -0.89% | 1 | 107 | Township |
| Gem | 13 | 94 | 97 | 0% | 281 | 0 | City |
| Kingery | 14 | 89 | 93 | -1.11% | 1 | 144 | Township |
| North Randall | 15 | 72 | 76 | -1.37% | 1 | 53 | Township |
| Menlo | 16 | 62 | 66 | -1.59% | 1 | 54 | Township |
| Wendell | 17 | 56 | 57 | 0% | 1 | 71 | Township |
Colby is the largest city in Thomas County, with a population of 5,504.
Wendell is the smallest city in Thomas County, with a population of 56.
There are 17 cities in Thomas County, Kansas.