30 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Washington | 1 | 50,071 | 48,717 | 0.63% | 2,346 | 21 | Township |
| Washington | 2 | 18,394 | 18,153 | 0.16% | 413 | 45 | Township |
| Phillipsburg | 3 | 15,448 | 15,205 | 0.36% | 4,841 | 3 | Town |
| Phillipsburg | 4 | 15,440 | 15,205 | 0.31% | 4,839 | 3 | Town |
| Hackettstown | 5 | 10,220 | 10,232 | 0.37% | 2,829 | 4 | Town |
| Hackettstown | 6 | 10,169 | 10,232 | -0.13% | 2,815 | 4 | Town |
| Lopatcong | 7 | 9,541 | 8,808 | 0.41% | 1,304 | 7 | Township |
| Washington | 8 | 9,522 | 9,271 | 0.9% | 3,225 | 3 | Township |
| Mansfield | 9 | 7,993 | 7,771 | 1.32% | 270 | 30 | Township |
| Washington | 10 | 7,396 | 7,288 | 0.28% | 3,764 | 2 | Borough |
| Washington | 11 | 7,395 | 7,288 | 0.27% | 3,763 | 2 | Borough |
| Washington | 12 | 7,066 | 6,490 | 2.01% | 393 | 18 | Township |
| Blairstown | 13 | 5,803 | 5,693 | 0.35% | 194 | 30 | Township |
| Independence | 14 | 5,772 | 5,460 | 2.14% | 291 | 20 | Township |
| Allamuchy | 15 | 5,491 | 5,347 | 0.29% | 275 | 20 | Township |
| White | 16 | 4,743 | 4,604 | 0.3% | 173 | 27 | Township |
| Delaware | 17 | 4,598 | 4,543 | 0.13% | 125 | 37 | Township |
| Pohatcong | 18 | 3,310 | 3,239 | 0.42% | 248 | 13 | Township |
| Knowlton | 19 | 2,948 | 2,887 | 0.31% | 119 | 25 | Township |
| Liberty | 20 | 2,706 | 2,667 | 0.22% | 232 | 12 | Township |
| Belvidere | 21 | 2,553 | 2,514 | 0.31% | 1,762 | 1 | Town |
| Belvidere | 22 | 2,552 | 2,514 | 0.28% | 1,761 | 1 | Town |
| Harmony | 23 | 2,550 | 2,491 | 0.47% | 107 | 24 | Township |
| Oxford | 24 | 2,485 | 2,442 | 0.32% | 417 | 6 | Township |
| Alpha | 25 | 2,365 | 2,324 | 0.34% | 1,407 | 2 | Borough |
| Alpha | 26 | 2,364 | 2,324 | 0.3% | 1,406 | 2 | Borough |
| Frelinghuysen | 27 | 2,253 | 2,201 | 0.49% | 95 | 24 | Township |
| Hope | 28 | 1,865 | 1,831 | 0.32% | 103 | 18 | Township |
| Hardwick | 29 | 1,635 | 1,591 | 0.74% | 44 | 38 | Township |
| Washington | 30 | 727 | 692 | 1.39% | 7 | 102 | Township |
Washington is the largest city in Warren County, with a population of 50,071.
Washington is the smallest city in Warren County, with a population of 727.
There are 30 cities in Warren County, New Jersey.