43 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Wellington | 1 | 7,492 | 7,682 | -0.5% | 983 | 7.62 | City |
| Belle Plaine township | 2 | 3,042 | 3,048 | -0.2% | 75 | 40.41 | Township |
| Oxford township | 3 | 2,040 | 2,030 | 0.05% | 737 | 2.77 | Township |
| Gore township | 4 | 2,002 | 1,861 | 1.21% | 63 | 31.87 | Township |
| Belle Plaine | 5 | 1,441 | 1,468 | -0.35% | 1,736 | 0.83 | City |
| Oxford township | 6 | 1,245 | 1,249 | -0.16% | 33 | 38.08 | Township |
| Conway township | 7 | 1,137 | 1,106 | 0.53% | 31 | 36.28 | Township |
| Conway Springs | 8 | 1,133 | 1,093 | 0.71% | 1,148 | 0.99 | City |
| Milton township | 9 | 1,052 | 1,047 | 0% | 29 | 36.35 | Township |
| Oxford | 10 | 1,040 | 1,044 | -0.1% | 1,148 | 0.91 | City |
| Caldwell | 11 | 996 | 1,026 | -0.6% | 921 | 1.08 | City |
| London township | 12 | 711 | 706 | 0.14% | 17 | 41.41 | Township |
| Springdale township | 13 | 674 | 665 | 0.15% | 19 | 35.81 | Township |
| Dixon township | 14 | 595 | 607 | -0.34% | 16 | 36.47 | Township |
| South Haven township | 15 | 535 | 533 | 0% | 10 | 54.01 | Township |
| Argonia | 16 | 445 | 459 | -0.67% | 638 | 0.70 | City |
| Eden township | 17 | 412 | 408 | 0.24% | 11 | 36.81 | Township |
| South Haven | 18 | 326 | 326 | 0% | 326 | 1 | City |
| Wellington township | 19 | 324 | 321 | 0.31% | 11 | 30.59 | Township |
| Milton township | 20 | 302 | 311 | -0.98% | 10 | 29.89 | Township |
| Avon township | 21 | 287 | 290 | -0.35% | 8 | 35.55 | Township |
| Harmon township | 22 | 251 | 256 | -0.79% | 8 | 30.61 | Township |
| Seventy-Six township | 23 | 234 | 228 | 0.43% | 7 | 35.30 | Township |
| Creek township | 24 | 197 | 199 | -0.51% | 5 | 36.63 | Township |
| Palestine township | 25 | 195 | 186 | 1.04% | 7 | 28.01 | Township |
| Illinois township | 26 | 170 | 171 | -0.58% | 5 | 36.40 | Township |
| Geuda Springs | 27 | 157 | 154 | 0.64% | 456 | 0.34 | City |
| Milton | 28 | 142 | 299 | -0.7% | 32 | 4.44 | CDP |
| Guelph township | 29 | 142 | 144 | -0.7% | 3 | 54.61 | Township |
| Ryan township | 30 | 141 | 144 | -0.7% | 4 | 35.54 | Township |
| Caldwell township | 31 | 140 | 140 | 0% | 3 | 52.54 | Township |
| Falls township | 32 | 136 | 133 | 0.74% | 3 | 53.54 | Township |
| Sumner township | 33 | 125 | 122 | 0% | 3 | 36.18 | Township |
| Jackson township | 34 | 122 | 124 | -0.81% | 3 | 36.34 | Township |
| Peck | 35 | 102 | 118 | 6.25% | 288 | 0.35 | CDP |
| Valverde township | 36 | 101 | 103 | -0.98% | 3 | 35.76 | Township |
| Greene township | 37 | 77 | 72 | 2.67% | 2 | 35.89 | Township |
| Mayfield | 38 | 73 | 73 | 0% | 247 | 0.30 | City |
| Bluff township | 39 | 60 | 61 | 0% | 1 | 52.60 | Township |
| Chikaskia township | 40 | 56 | 55 | 0% | 2 | 36.17 | Township |
| Milan | 41 | 51 | 53 | 0% | 386 | 0.13 | City |
| Hunnewell | 42 | 43 | 42 | 0% | 77 | 0.56 | City |
| Morris township | 43 | 18 | 18 | 0% | 0.00 | 36.48 | Township |
Wellington is the largest city in Sumner County, with a population of 7,492.
Morris township is the smallest city in Sumner County.
There are 43 cities in Sumner County, Kansas.