| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Franklin | 1 | 68,980 | 68,178 | -0.18% | 1,494 | 46 | Township |
| Vernon | 2 | 23,053 | 22,292 | 0.38% | 341 | 68 | Township |
| Sparta | 3 | 20,525 | 19,616 | 0.46% | 559 | 37 | Township |
| Franklin | 4 | 16,677 | 16,365 | 0.07% | 299 | 56 | Township |
| Hopatcong | 5 | 14,897 | 14,333 | 0.49% | 1,369 | 11 | Borough |
| Wantage | 6 | 11,219 | 10,792 | 0.58% | 168 | 67 | Township |
| Hardyston | 7 | 8,592 | 8,132 | 0.6% | 269 | 32 | Township |
| Newton | 8 | 8,504 | 8,326 | 0.21% | 2,531 | 3 | Town |
| Byram | 9 | 8,281 | 8,006 | 0.39% | 385 | 22 | Township |
| Andover | 10 | 5,749 | 5,998 | 0.49% | 287 | 20 | Township |
| Frankford | 11 | 5,381 | 5,289 | 0.24% | 159 | 34 | Township |
| Franklin | 12 | 5,106 | 4,896 | 0.45% | 1,172 | 4 | Borough |
| Stillwater | 13 | 4,052 | 3,989 | -0.49% | 150 | 27 | Township |
| Montague | 14 | 3,913 | 3,777 | 0.44% | 87 | 45 | Township |
| Green | 15 | 3,729 | 3,594 | 0.38% | 233 | 16 | Township |
| Stanhope | 16 | 3,631 | 3,514 | 0.47% | 1,976 | 2 | Borough |
| Hamburg | 17 | 3,356 | 3,242 | 0.33% | 2,931 | 1 | Borough |
| Fredon | 18 | 3,351 | 3,228 | 0.57% | 190 | 18 | Township |
| Franklin | 19 | 3,308 | 3,244 | 0.61% | 144 | 23 | Township |
| Franklin | 20 | 3,049 | 2,984 | 0% | 130 | 23 | Township |
| Lafayette | 21 | 2,429 | 2,325 | 0.5% | 136 | 18 | Township |
| Ogdensburg | 22 | 2,328 | 2,252 | 0.39% | 1,056 | 2 | Borough |
| Sussex | 23 | 2,087 | 2,019 | 0.38% | 3,519 | 1 | Borough |
| Sandyston | 24 | 2,040 | 1,977 | 0.39% | 49 | 41 | Township |
| Branchville | 25 | 812 | 782 | 0.37% | 1,369 | 1 | Borough |
| Andover | 26 | 616 | 596 | 0.33% | 457 | 1 | Borough |
| Walpack | 27 | 8 | 8 | 0% | 0 | 24 | Township |
Franklin is the largest city in Sussex County, with a population of 68,980.
Walpack is the smallest city in Sussex County, with a population of 8.
There are 27 cities in Sussex County, New Jersey.