| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Ottawa | 1 | 12,736 | 12,632 | 0.16% | 1,195 | 11 | City |
| Wellsville | 2 | 1,998 | 1,947 | -0.2% | 1,162 | 2 | City |
| Pomona | 3 | 882 | 888 | 0% | 934 | 1 | City |
| Richmond | 4 | 437 | 451 | -0.68% | 1,282 | 0 | City |
| Williamsburg | 5 | 381 | 389 | -0.52% | 390 | 1 | City |
| Princeton | 6 | 256 | 247 | 0.39% | 757 | 0 | City |
| Lane | 7 | 244 | 240 | 0% | 1,047 | 0 | City |
| Rantoul | 8 | 173 | 169 | 0.58% | 1,177 | 0 | City |
Ottawa is the largest city in Franklin County, with a population of 12,736.
Rantoul is the smallest city in Franklin County, with a population of 173.
There are 8 cities in Franklin County, Kansas.