23 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Chambersburg | 1 | 23,622 | 21,879 | 1.25% | 3,411 | 7 | Borough |
| Concord | 2 | 18,756 | 18,276 | 0.82% | 1,377 | 14 | Township |
| Greene | 3 | 18,693 | 18,435 | 0.16% | 326 | 57 | Township |
| Antrim | 4 | 16,648 | 15,801 | 1.06% | 238 | 70 | Township |
| Guilford | 5 | 15,403 | 14,654 | 1.14% | 301 | 51 | Township |
| Waynesboro | 6 | 11,137 | 11,029 | 0.16% | 3,246 | 3 | Borough |
| St. Thomas | 7 | 6,022 | 5,915 | 0.23% | 116 | 52 | Township |
| Quincy | 8 | 5,295 | 5,305 | -0.11% | 117 | 45 | Township |
| Peters | 9 | 4,468 | 4,465 | -0.02% | 80 | 56 | Township |
| Greencastle | 10 | 4,225 | 4,228 | 0% | 2,661 | 2 | Borough |
| Letterkenny | 11 | 2,586 | 2,462 | 1.13% | 37 | 70 | Township |
| Fannett | 12 | 2,491 | 2,486 | -0.12% | 37 | 68 | Township |
| Lurgan | 13 | 2,191 | 2,206 | -0.09% | 67 | 33 | Township |
| Marion | 14 | 1,981 | 1,841 | 0.61% | 131 | 15 | Township |
| Metal | 15 | 1,755 | 1,759 | -0.23% | 39 | 45 | Township |
| Mont Alto | 16 | 1,557 | 1,575 | -0.19% | 2,766 | 1 | Borough |
| Mercersburg | 17 | 1,487 | 1,505 | -0.2% | 1,649 | 1 | Borough |
| Concord | 18 | 1,356 | 1,410 | -0.44% | 56 | 24 | Township |
| Concord | 19 | 1,255 | 1,279 | -0.08% | 38 | 33 | Township |
| Marion | 20 | 1,211 | 1,186 | 0.33% | 55 | 22 | Township |
| Marion | 21 | 1,112 | 1,152 | -0.71% | 44 | 25 | Township |
| Marion | 22 | 790 | 798 | 0% | 77 | 10 | Township |
| Orrstown | 23 | 212 | 214 | 0% | 3,313 | 0 | Borough |
Chambersburg is the largest city in Franklin County, with a population of 23,622.
Orrstown is the smallest city in Franklin County, with a population of 212.
There are 23 cities in Franklin County, Pennsylvania.