27 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Ottawa | 1 | 12,718 | 12,638 | 0.13% | 1,232 | 10.32 | City |
| Wellsville | 2 | 1,918 | 1,947 | -0.31% | 1,116 | 1.72 | City |
| Pomona township | 3 | 1,135 | 1,127 | 0.18% | 55 | 20.65 | Township |
| Centropolis township | 4 | 1,040 | 1,022 | 0.48% | 26 | 40.52 | Township |
| Pomona | 5 | 892 | 887 | 0.11% | 945 | 0.94 | City |
| Ottawa township | 6 | 842 | 818 | 0.84% | 20 | 41.68 | Township |
| Cutler township | 7 | 821 | 792 | 1.11% | 19 | 42.68 | Township |
| Richmond township | 8 | 809 | 813 | 0.12% | 23 | 34.78 | Township |
| Ohio township | 9 | 772 | 744 | 0.92% | 19 | 41.59 | Township |
| Williamsburg township | 10 | 710 | 705 | 0.42% | 13 | 55.77 | Township |
| Peoria township | 11 | 678 | 654 | 1.04% | 19 | 35.31 | Township |
| Pottawatomie township | 12 | 613 | 590 | 1.16% | 16 | 38.55 | Township |
| Homewood township | 13 | 556 | 540 | 0.91% | 19 | 30.05 | Township |
| Richmond township | 14 | 480 | 498 | -0.62% | 14 | 33.96 | Township |
| Harrison township | 15 | 450 | 441 | 0.67% | 18 | 25.31 | Township |
| Hayes township | 16 | 442 | 433 | 0.68% | 15 | 29.71 | Township |
| Richmond | 17 | 435 | 449 | -0.68% | 1,276 | 0.34 | City |
| Greenwood township | 18 | 399 | 390 | 0.76% | 13 | 30.39 | Township |
| Williamsburg | 19 | 384 | 389 | -0.26% | 393 | 0.98 | City |
| Appanoose township | 20 | 328 | 319 | 0.92% | 11 | 29.77 | Township |
| Princeton | 21 | 258 | 247 | 0.78% | 663 | 0.39 | City |
| Lane | 22 | 248 | 243 | 0.4% | 1,064 | 0.23 | City |
| Rantoul | 23 | 173 | 167 | 0.58% | 1,177 | 0.15 | City |
| Centropolis | 24 | 115 | 149 | 7.48% | 343 | 0.34 | CDP |
| Lane township | 25 | 107 | 104 | 0.94% | 3 | 35.85 | Township |
| Lane township | 26 | 76 | 78 | 0% | 1 | 53.47 | Township |
| Ottawa township | 27 | 35 | 35 | 0% | 1 | 35.88 | Township |
Ottawa is the largest city in Franklin County, with a population of 12,718.
Ottawa township is the smallest city in Franklin County.
There are 27 cities in Franklin County, Kansas.