| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Chambersburg | 1 | 23,664 | 21,882 | 1.23% | 3,417 | 7 | Borough |
| Greene | 2 | 18,751 | 18,431 | 0.16% | 327 | 57 | Township |
| Concord | 3 | 18,593 | 18,273 | 0.63% | 1,365 | 14 | Township |
| Antrim | 4 | 16,627 | 15,805 | 0.89% | 237 | 70 | Township |
| Guilford | 5 | 15,688 | 14,639 | 2.06% | 307 | 51 | Township |
| Waynesboro | 6 | 11,209 | 11,016 | 0.17% | 3,267 | 3 | Borough |
| St. Thomas | 7 | 6,049 | 5,917 | 0.37% | 117 | 52 | Township |
| Quincy | 8 | 5,282 | 5,307 | -0.02% | 117 | 45 | Township |
| Peters | 9 | 4,472 | 4,455 | -0.02% | 80 | 56 | Township |
| Greencastle | 10 | 4,221 | 4,224 | -0.02% | 2,658 | 2 | Borough |
| Letterkenny | 11 | 2,572 | 2,460 | 0.86% | 37 | 70 | Township |
| Fannett | 12 | 2,500 | 2,485 | 0.08% | 37 | 68 | Township |
| Lurgan | 13 | 2,214 | 2,206 | 0.27% | 68 | 33 | Township |
| Marion | 14 | 1,969 | 1,843 | 0.36% | 131 | 15 | Township |
| Metal | 15 | 1,774 | 1,761 | 0.11% | 40 | 45 | Township |
| Mont Alto | 16 | 1,560 | 1,575 | -0.19% | 2,771 | 1 | Borough |
| Mercersburg | 17 | 1,489 | 1,506 | -0.2% | 1,651 | 1 | Borough |
| Concord | 18 | 1,345 | 1,403 | -0.66% | 56 | 24 | Township |
| Concord | 19 | 1,246 | 1,276 | -0.24% | 38 | 33 | Township |
| Marion | 20 | 1,196 | 1,183 | 0.25% | 54 | 22 | Township |
| Marion | 21 | 1,102 | 1,141 | -0.72% | 43 | 25 | Township |
| Marion | 22 | 796 | 802 | 0.13% | 78 | 10 | Township |
| Orrstown | 23 | 209 | 214 | -0.48% | 3,266 | 0 | Borough |
Chambersburg is the largest city in Franklin County, with a population of 23,664.
Orrstown is the smallest city in Franklin County, with a population of 209.
There are 23 cities in Franklin County, Pennsylvania.