41 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 | 3,028 | 3,051 | -0.3% | 75 | 40 | Township |
| Oxford | 3 | 2,076 | 2,030 | 0.68% | 750 | 3 | Township |
| Gore | 4 | 1,961 | 1,862 | 0.05% | 62 | 32 | Township |
| Belle Plaine | 5 | 1,432 | 1,470 | -0.42% | 1,725 | 1 | City |
| Oxford | 6 | 1,230 | 1,247 | -0.57% | 32 | 38 | Township |
| Conway | 7 | 1,156 | 1,107 | 0.7% | 32 | 36 | Township |
| Conway Springs | 8 | 1,155 | 1,095 | 0.87% | 1,170 | 1 | City |
| Oxford | 9 | 1,033 | 1,041 | -0.1% | 1,140 | 1 | City |
| Milton | 10 | 1,008 | 1,048 | -1.47% | 28 | 36 | Township |
| Caldwell | 11 | 988 | 1,023 | -0.6% | 914 | 1 | City |
| London | 12 | 711 | 706 | 0% | 17 | 41 | Township |
| Springdale | 13 | 688 | 668 | 0.44% | 19 | 36 | Township |
| Dixon | 14 | 589 | 604 | -0.51% | 16 | 36 | Township |
| South Haven | 15 | 531 | 531 | -0.19% | 10 | 54 | Township |
| Argonia | 16 | 442 | 456 | -0.45% | 633 | 1 | City |
| Eden | 17 | 408 | 407 | 0% | 11 | 37 | Township |
| South Haven | 18 | 325 | 325 | 0% | 325 | 1 | City |
| Wellington | 19 | 319 | 320 | -0.31% | 10 | 31 | Township |
| Milton | 20 | 305 | 311 | -0.65% | 10 | 30 | Township |
| Avon | 21 | 292 | 289 | 0.34% | 8 | 36 | Township |
| Harmon | 22 | 257 | 254 | 0.39% | 8 | 31 | Township |
| Seventy-Six | 23 | 232 | 230 | -0.43% | 7 | 35 | Township |
| Creek | 24 | 198 | 200 | -0.5% | 5 | 37 | Township |
| Palestine | 25 | 184 | 186 | -0.54% | 7 | 28 | Township |
| Illinois | 26 | 171 | 170 | 0% | 5 | 36 | Township |
| Geuda Springs | 27 | 154 | 154 | 0% | 448 | 0 | City |
| Caldwell | 28 | 143 | 143 | 0% | 3 | 53 | Township |
| Guelph | 29 | 142 | 144 | -0.7% | 3 | 55 | Township |
| Ryan | 30 | 141 | 141 | 0% | 4 | 36 | Township |
| Falls | 31 | 136 | 133 | 0.74% | 3 | 54 | Township |
| Sumner | 32 | 132 | 123 | 1.54% | 4 | 36 | Township |
| Jackson | 33 | 122 | 124 | -0.81% | 3 | 36 | Township |
| Valverde | 34 | 102 | 104 | -0.97% | 3 | 36 | Township |
| Mayfield | 35 | 73 | 73 | 0% | 247 | 0 | City |
| Greene | 36 | 71 | 72 | -1.39% | 2 | 36 | Township |
| Bluff | 37 | 64 | 59 | 3.23% | 1 | 53 | Township |
| Chikaskia | 38 | 60 | 55 | 3.45% | 2 | 36 | Township |
| Milan | 39 | 52 | 52 | 0% | 394 | 0 | City |
| Hunnewell | 40 | 43 | 42 | 0% | 77 | 1 | City |
| Morris | 41 | 19 | 19 | 0% | 1 | 36 | Township |
Wellington is the largest city in Sumner County, with a population of 7,500.
Morris is the smallest city in Sumner County, with a population of 19.
There are 41 cities in Sumner County, Kansas.