Note: As defined by the US Census Bureau, a city's official boundaries often extend miles beyond the city itself and may even cross county lines. As such, several thousand US cities officially exist in two or more counties (and therefore appear on multiple counties' lists of cities.)
City | Rank | 2024 Pop. | 2020 Pop. | Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Franklin township | 1 | 67,981 | 68,312 | -0.37% | 1,472 | 46.2 | Township |
| Vernon township | 2 | 22,820 | 22,296 | 0.48% | 338 | 67.5 | Township |
| Sparta township | 3 | 20,302 | 19,623 | 0.53% | 553 | 36.7 | Township |
| Franklin township | 4 | 16,621 | 16,371 | 0.47% | 298 | 55.8 | Township |
| Hopatcong borough | 5 | 14,701 | 14,328 | 0.54% | 1,351 | 10.9 | Borough |
| Wantage township | 6 | 11,046 | 10,793 | 0.48% | 165 | 66.8 | Township |
| Hardyston township | 7 | 8,500 | 8,112 | 1.08% | 266 | 31.9 | Township |
| Byram township | 8 | 8,187 | 8,005 | 0.43% | 380 | 21.5 | Township |
| Newton | 9 | 8,103 | 8,344 | -1.66% | 2,412 | 3.4 | Town |
| Andover township | 10 | 5,663 | 5,996 | 0.5% | 283 | 20.0 | Township |
| Frankford township | 11 | 5,291 | 5,291 | -0.24% | 156 | 33.9 | Township |
| Franklin borough | 12 | 5,051 | 4,894 | 0.86% | 1,160 | 4.4 | Borough |
| Stillwater township | 13 | 4,077 | 3,990 | 0.34% | 151 | 26.9 | Township |
| Montague township | 14 | 3,874 | 3,779 | 0.62% | 86 | 45.2 | Township |
| Green township | 15 | 3,703 | 3,605 | 0.54% | 231 | 16.0 | Township |
| Stanhope borough | 16 | 3,592 | 3,517 | 0.48% | 1,954 | 1.8 | Borough |
| Hamburg borough | 17 | 3,352 | 3,263 | 0.63% | 2,928 | 1.1 | Borough |
| Fredon township | 18 | 3,308 | 3,231 | 0.46% | 188 | 17.6 | Township |
| Franklin township | 19 | 3,276 | 3,254 | -0.3% | 142 | 23.0 | Township |
| Franklin township | 20 | 3,007 | 2,965 | 0.23% | 128 | 23.4 | Township |
| Lafayette township | 21 | 2,416 | 2,345 | 0.67% | 135 | 17.9 | Township |
| Ogdensburg borough | 22 | 2,304 | 2,252 | 0.48% | 1,045 | 2.2 | Borough |
| Sussex borough | 23 | 2,059 | 2,014 | 0.44% | 3,472 | 0.6 | Borough |
| Sandyston township | 24 | 2,016 | 1,974 | 0.5% | 49 | 41.3 | Township |
Note: City markers shown outside the county boundary mean that a part of the city extends into this county, but is primarily located in an adjacent county.
Franklin township is the largest city in Sussex County.
Sandyston township is the smallest city in Sussex County.
There are 24 cities in Sussex County, New Jersey.