23 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Elizabeth | 1 | 145,149 | 136,681 | 1.66% | 11,783 | 12 | City |
| Union | 2 | 66,207 | 59,829 | 2.35% | 7,315 | 9 | Township |
| Plainfield | 3 | 58,399 | 54,344 | 1.65% | 9,800 | 6 | City |
| Linden | 4 | 46,839 | 43,540 | 1.57% | 4,382 | 11 | City |
| Westfield | 5 | 34,022 | 30,898 | 2.98% | 5,060 | 7 | Town |
| Rahway | 6 | 31,685 | 29,671 | 1.48% | 8,133 | 4 | City |
| Scotch Plains | 7 | 26,005 | 24,855 | 1.53% | 2,883 | 9 | Township |
| Cranford | 8 | 25,285 | 23,815 | 1.55% | 5,230 | 5 | Township |
| Summit | 9 | 23,884 | 22,639 | 1.66% | 3,985 | 6 | City |
| Roselle | 10 | 23,776 | 22,606 | 1.52% | 9,023 | 3 | Borough |
| Hillside | 11 | 23,370 | 22,342 | 1.48% | 8,446 | 3 | Township |
| Springfield | 12 | 18,646 | 17,106 | 2.8% | 3,616 | 5 | Township |
| Clark | 13 | 17,481 | 15,464 | 3.57% | 4,091 | 4 | Township |
| Berkeley Heights | 14 | 16,554 | 13,203 | 6.58% | 2,661 | 6 | Township |
| Roselle Park | 15 | 14,844 | 14,005 | 1.55% | 12,118 | 1 | Borough |
| New Providence | 16 | 14,407 | 13,704 | 1.59% | 3,906 | 4 | Borough |
| Kenilworth | 17 | 8,793 | 8,392 | 1.54% | 4,095 | 2 | Borough |
| Fanwood | 18 | 8,340 | 7,749 | 2.28% | 6,224 | 1 | Borough |
| Mountainside | 19 | 7,606 | 6,992 | 2.55% | 1,903 | 4 | Borough |
| Union | 20 | 6,806 | 6,495 | 2.02% | 363 | 19 | Township |
| Garwood | 21 | 5,544 | 4,430 | 1.82% | 8,529 | 1 | Borough |
| Springfield | 22 | 3,355 | 3,239 | 0.93% | 114 | 30 | Township |
| Winfield | 23 | 1,484 | 1,415 | 1.57% | 8,199 | 0 | Township |
Elizabeth is the largest city in Union County, with a population of 145,149.
Winfield is the smallest city in Union County, with a population of 1,484.
There are 23 cities in Union County, New Jersey.