30 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Washington | 1 | 50,386 | 48,717 | 0.63% | 2,360 | 21 | Township |
| Washington | 2 | 18,424 | 18,153 | 0.16% | 413 | 45 | Township |
| Phillipsburg | 3 | 15,503 | 15,205 | 0.36% | 4,858 | 3 | Town |
| Phillipsburg | 4 | 15,487 | 15,205 | 0.3% | 4,853 | 3 | Town |
| Hackettstown | 5 | 10,258 | 10,232 | 0.37% | 2,840 | 4 | Town |
| Hackettstown | 6 | 10,157 | 10,232 | -0.12% | 2,812 | 4 | Town |
| Washington | 7 | 9,607 | 9,271 | 0.89% | 3,253 | 3 | Township |
| Lopatcong | 8 | 9,580 | 8,808 | 0.41% | 1,309 | 7 | Township |
| Mansfield | 9 | 8,097 | 7,771 | 1.3% | 274 | 30 | Township |
| Washington | 10 | 7,418 | 7,288 | 0.3% | 3,775 | 2 | Borough |
| Washington | 11 | 7,415 | 7,288 | 0.27% | 3,774 | 2 | Borough |
| Washington | 12 | 7,205 | 6,490 | 1.97% | 401 | 18 | Township |
| Independence | 13 | 5,893 | 5,460 | 2.1% | 297 | 20 | Township |
| Blairstown | 14 | 5,823 | 5,693 | 0.34% | 195 | 30 | Township |
| Allamuchy | 15 | 5,507 | 5,347 | 0.29% | 275 | 20 | Township |
| White | 16 | 4,757 | 4,604 | 0.3% | 174 | 27 | Township |
| Delaware | 17 | 4,604 | 4,543 | 0.13% | 126 | 37 | Township |
| Pohatcong | 18 | 3,324 | 3,239 | 0.42% | 249 | 13 | Township |
| Knowlton | 19 | 2,957 | 2,887 | 0.31% | 120 | 25 | Township |
| Liberty | 20 | 2,712 | 2,667 | 0.22% | 232 | 12 | Township |
| Harmony | 21 | 2,562 | 2,491 | 0.47% | 108 | 24 | Township |
| Belvidere | 22 | 2,561 | 2,514 | 0.31% | 1,767 | 1 | Town |
| Belvidere | 23 | 2,560 | 2,514 | 0.31% | 1,767 | 1 | Town |
| Oxford | 24 | 2,493 | 2,442 | 0.32% | 418 | 6 | Township |
| Alpha | 25 | 2,373 | 2,324 | 0.34% | 1,412 | 2 | Borough |
| Alpha | 26 | 2,371 | 2,324 | 0.3% | 1,410 | 2 | Borough |
| Frelinghuysen | 27 | 2,264 | 2,201 | 0.49% | 96 | 24 | Township |
| Hope | 28 | 1,871 | 1,831 | 0.32% | 103 | 18 | Township |
| Hardwick | 29 | 1,647 | 1,591 | 0.73% | 44 | 38 | Township |
| Washington | 30 | 737 | 692 | 1.38% | 7 | 102 | Township |
Washington is the largest city in Warren County, with a population of 50,386.
Washington is the smallest city in Warren County, with a population of 737.
There are 30 cities in Warren County, New Jersey.