36 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Franklin | 1 | 70,857 | 68,315 | 1.42% | 1,535 | 46 | Township |
| Vernon | 2 | 23,027 | 22,291 | 0.65% | 341 | 68 | Township |
| Sparta | 3 | 20,507 | 19,623 | 0.71% | 558 | 37 | Township |
| Franklin | 4 | 16,815 | 16,374 | 0.74% | 301 | 56 | Township |
| Hopatcong | 5 | 14,860 | 14,330 | 0.75% | 1,366 | 11 | Borough |
| Hopatcong | 6 | 14,855 | 14,330 | 0.71% | 1,365 | 11 | Borough |
| Wantage | 7 | 11,174 | 10,788 | 0.78% | 167 | 67 | Township |
| Newton | 8 | 8,620 | 8,346 | 2.19% | 2,565 | 3 | Town |
| Hardyston | 9 | 8,525 | 8,114 | 0.63% | 267 | 32 | Township |
| Newton | 10 | 8,457 | 8,346 | 0.26% | 2,517 | 3 | Town |
| Byram | 11 | 8,274 | 8,005 | 0.69% | 384 | 22 | Township |
| Andover | 12 | 5,731 | 5,995 | 0.81% | 286 | 20 | Township |
| Frankford | 13 | 5,382 | 5,296 | 0.62% | 159 | 34 | Township |
| Franklin | 14 | 5,102 | 4,896 | 0.85% | 1,171 | 4 | Borough |
| Franklin | 15 | 5,099 | 4,896 | 0.79% | 1,171 | 4 | Borough |
| Stillwater | 16 | 4,119 | 3,990 | 0.64% | 153 | 27 | Township |
| Montague | 17 | 3,906 | 3,778 | 0.67% | 86 | 45 | Township |
| Green | 18 | 3,738 | 3,605 | 0.7% | 233 | 16 | Township |
| Stanhope | 19 | 3,622 | 3,515 | 0.64% | 1,971 | 2 | Borough |
| Stanhope | 20 | 3,620 | 3,515 | 0.58% | 1,970 | 2 | Borough |
| Hamburg | 21 | 3,374 | 3,258 | 0.69% | 2,947 | 1 | Borough |
| Hamburg | 22 | 3,372 | 3,258 | 0.63% | 2,945 | 1 | Borough |
| Fredon | 23 | 3,337 | 3,230 | 0.63% | 189 | 18 | Township |
| Franklin | 24 | 3,314 | 3,256 | 0.21% | 144 | 23 | Township |
| Franklin | 25 | 3,035 | 2,967 | 0.46% | 130 | 23 | Township |
| Lafayette | 26 | 2,451 | 2,349 | 0.91% | 137 | 18 | Township |
| Ogdensburg | 27 | 2,324 | 2,252 | 0.61% | 1,054 | 2 | Borough |
| Ogdensburg | 28 | 2,324 | 2,252 | 0.61% | 1,054 | 2 | Borough |
| Sussex | 29 | 2,085 | 2,019 | 0.63% | 3,516 | 1 | Borough |
| Sussex | 30 | 2,085 | 2,019 | 0.63% | 3,516 | 1 | Borough |
| Sandyston | 31 | 2,034 | 1,975 | 0.59% | 49 | 41 | Township |
| Branchville | 32 | 816 | 786 | 0.74% | 1,376 | 1 | Borough |
| Branchville | 33 | 815 | 786 | 0.62% | 1,374 | 1 | Borough |
| Andover | 34 | 614 | 594 | 0.66% | 455 | 1 | Borough |
| Andover | 35 | 614 | 594 | 0.66% | 455 | 1 | Borough |
| Walpack | 36 | 7 | 7 | 0% | 0.00 | 24 | Township |
Franklin is the largest city in Sussex County, with a population of 70,857.
Walpack is the smallest city in Sussex County, with a population of 7.
There are 36 cities in Sussex County, New Jersey.