23 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Chambersburg | 1 | 23,331 | 21,879 | 1.26% | 3,369 | 7 | Borough |
| Greene | 2 | 18,664 | 18,435 | 0.16% | 326 | 57 | Township |
| Concord | 3 | 18,603 | 18,276 | 0.83% | 1,365 | 14 | Township |
| Antrim | 4 | 16,473 | 15,801 | 1.07% | 235 | 70 | Township |
| Guilford | 5 | 15,229 | 14,654 | 1.16% | 298 | 51 | Township |
| Waynesboro | 6 | 11,119 | 11,029 | 0.16% | 3,241 | 3 | Borough |
| St. Thomas | 7 | 6,008 | 5,915 | 0.23% | 116 | 52 | Township |
| Quincy | 8 | 5,301 | 5,305 | -0.11% | 117 | 45 | Township |
| Peters | 9 | 4,469 | 4,465 | -0.02% | 80 | 56 | Township |
| Greencastle | 10 | 4,225 | 4,228 | -0.02% | 2,661 | 2 | Borough |
| Letterkenny | 11 | 2,557 | 2,462 | 1.15% | 36 | 70 | Township |
| Fannett | 12 | 2,494 | 2,486 | -0.12% | 37 | 68 | Township |
| Lurgan | 13 | 2,193 | 2,206 | -0.09% | 67 | 33 | Township |
| Marion | 14 | 1,969 | 1,841 | 0.61% | 131 | 15 | Township |
| Metal | 15 | 1,759 | 1,759 | -0.23% | 39 | 45 | Township |
| Mont Alto | 16 | 1,560 | 1,575 | -0.19% | 2,771 | 1 | Borough |
| Mercersburg | 17 | 1,490 | 1,505 | -0.2% | 1,652 | 1 | Borough |
| Concord | 18 | 1,362 | 1,410 | -0.44% | 56 | 24 | Township |
| Concord | 19 | 1,256 | 1,279 | -0.08% | 38 | 33 | Township |
| Marion | 20 | 1,207 | 1,186 | 0.33% | 55 | 22 | Township |
| Marion | 21 | 1,120 | 1,152 | -0.71% | 44 | 25 | Township |
| Marion | 22 | 790 | 798 | 0% | 77 | 10 | Township |
| Orrstown | 23 | 212 | 214 | -0.47% | 3,313 | 0 | Borough |
Chambersburg is the largest city in Franklin County, with a population of 23,331.
Orrstown is the smallest city in Franklin County, with a population of 212.
There are 23 cities in Franklin County, Pennsylvania.