35 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Colby | 1 | 5,521 | 5,607 | -0.32% | 1,508 | 4 | City |
| Colby | 2 | 5,521 | 5,609 | -0.32% | 1,508 | 4 | City |
| Morgan | 3 | 536 | 560 | -1.29% | 5 | 104 | Township |
| Morgan | 4 | 536 | 560 | -1.29% | 5 | 104 | Township |
| West Hale | 5 | 342 | 353 | -0.58% | 6 | 54 | Township |
| West Hale | 6 | 342 | 353 | -0.58% | 6 | 54 | Township |
| Brewster | 7 | 280 | 290 | -0.71% | 1,085 | 0 | City |
| Brewster | 8 | 280 | 290 | -0.71% | 1,085 | 0 | City |
| Smith | 9 | 238 | 244 | -0.42% | 7 | 36 | Township |
| Smith | 10 | 238 | 244 | -0.42% | 7 | 36 | Township |
| South Randall | 11 | 206 | 215 | -0.96% | 2 | 107 | Township |
| South Randall | 12 | 206 | 215 | -0.96% | 2 | 107 | Township |
| Rexford | 13 | 196 | 201 | -0.51% | 751 | 0 | City |
| Rexford | 14 | 196 | 201 | -0.51% | 751 | 0 | City |
| Summers | 15 | 165 | 172 | -0.6% | 1 | 144 | Township |
| Summers | 16 | 165 | 172 | -0.6% | 1 | 144 | Township |
| Lacey | 17 | 125 | 129 | -0.79% | 4 | 36 | Township |
| Lacey | 18 | 125 | 129 | -0.79% | 4 | 36 | Township |
| Rovohl | 19 | 122 | 126 | -0.81% | 1 | 107 | Township |
| Rovohl | 20 | 122 | 126 | -0.81% | 1 | 107 | Township |
| East Hale | 21 | 115 | 117 | -0.86% | 2 | 54 | Township |
| East Hale | 22 | 115 | 117 | -0.86% | 2 | 54 | Township |
| Barrett | 23 | 112 | 116 | -0.88% | 1 | 107 | Township |
| Barrett | 24 | 112 | 116 | -0.88% | 1 | 107 | Township |
| Levant | 25 | 112 | 49 | 6.67% | 111 | 1 | CDP |
| Gem | 26 | 94 | 97 | -1.05% | 281 | 0 | City |
| Gem | 27 | 94 | 97 | -1.05% | 281 | 0 | City |
| Kingery | 28 | 90 | 93 | -1.1% | 1 | 144 | Township |
| Kingery | 29 | 90 | 93 | -1.1% | 1 | 144 | Township |
| North Randall | 30 | 73 | 76 | -1.35% | 1 | 53 | Township |
| North Randall | 31 | 73 | 76 | -1.35% | 1 | 53 | Township |
| Menlo | 32 | 63 | 66 | -1.56% | 1 | 54 | Township |
| Menlo | 33 | 63 | 66 | -1.56% | 1 | 54 | Township |
| Wendell | 34 | 56 | 57 | 0% | 1 | 71 | Township |
| Wendell | 35 | 56 | 57 | 0% | 1 | 71 | Township |
Colby is the largest city in Thomas County, with a population of 5,521.
Wendell is the smallest city in Thomas County, with a population of 56.
There are 35 cities in Thomas County, Kansas.