City | Rank | 2026 Pop.↓ | 2020 Pop. | Annual Change | Density /mi² | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Phillipsburg | 1 | 15,453 | 15,196 | -0.02% | 4,843 | 3 | Town |
| Hackettstown | 2 | 10,170 | 10,222 | -0.15% | 2,816 | 4 | Town |
| Lopatcong | 3 | 9,527 | 8,810 | -0.1% | 1,302 | 7 | Township |
| Mansfield | 4 | 8,070 | 7,694 | 0.93% | 273 | 30 | Township |
| Washington | 5 | 7,306 | 7,232 | -0.27% | 3,718 | 2 | Borough |
| Washington | 6 | 7,214 | 6,539 | 1.49% | 402 | 18 | Township |
| Blairstown | 7 | 5,822 | 5,696 | 0.12% | 195 | 30 | Township |
| Independence | 8 | 5,656 | 5,464 | -0.18% | 285 | 20 | Township |
| Allamuchy | 9 | 5,474 | 5,347 | -0.18% | 274 | 20 | Township |
| White | 10 | 4,697 | 4,606 | -0.19% | 172 | 27 | Township |
| Delaware | 11 | 4,623 | 4,545 | 0.57% | 126 | 37 | Township |
| Pohatcong | 12 | 3,850 | 3,236 | 7.6% | 288 | 13 | Township |
| Knowlton | 13 | 2,942 | 2,889 | -0.17% | 119 | 25 | Township |
| Liberty | 14 | 2,694 | 2,665 | -0.26% | 231 | 12 | Township |
| Belvidere | 15 | 2,546 | 2,515 | -0.2% | 1,757 | 1 | Town |
| Harmony | 16 | 2,540 | 2,487 | -0.08% | 107 | 24 | Township |
| Oxford | 17 | 2,453 | 2,441 | -0.65% | 412 | 6 | Township |
| Alpha | 18 | 2,358 | 2,325 | -0.17% | 1,403 | 2 | Borough |
| Frelinghuysen | 19 | 2,238 | 2,189 | -0.04% | 95 | 24 | Township |
| Hope | 20 | 1,869 | 1,845 | -0.32% | 103 | 18 | Township |
| Hardwick | 21 | 1,639 | 1,592 | 0.24% | 44 | 38 | Township |
Phillipsburg is the largest city in Warren County, with a population of 15,453.
Hardwick is the smallest city in Warren County, with a population of 1,639.
There are 21 cities in Warren County, New Jersey.