11 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Wellington | 1 | 7,500 | 7,682 | -0.4% | 985 | 8 | City |
| Belle Plaine | 2 | 1,432 | 1,470 | -0.42% | 1,725 | 1 | City |
| Conway Springs | 3 | 1,155 | 1,095 | 0.87% | 1,170 | 1 | City |
| Oxford | 4 | 1,033 | 1,041 | -0.1% | 1,140 | 1 | City |
| Caldwell | 5 | 988 | 1,023 | -0.6% | 914 | 1 | City |
| Argonia | 6 | 442 | 456 | -0.45% | 633 | 1 | City |
| South Haven | 7 | 325 | 325 | 0% | 325 | 1 | City |
| Geuda Springs | 8 | 154 | 154 | 0% | 448 | 0 | City |
| Mayfield | 9 | 73 | 73 | 0% | 247 | 0 | City |
| Milan | 10 | 52 | 52 | 0% | 394 | 0 | City |
| Hunnewell | 11 | 43 | 42 | 0% | 77 | 1 | City |
Wellington is the largest city in Sumner County, with a population of 7,500.
Hunnewell is the smallest city in Sumner County, with a population of 43.
There are 11 cities in Sumner County, Kansas.