36 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 |
| Elizabeth | 2 | 142,279 | 136,681 | 0.66% | 11,550 | 12 | City |
| Union | 3 | 66,207 | 59,829 | 2.35% | 7,315 | 9 | Township |
| Plainfield | 4 | 58,399 | 54,344 | 1.65% | 9,800 | 6 | City |
| Plainfield | 5 | 57,588 | 54,344 | 0.95% | 9,664 | 6 | City |
| Linden | 6 | 46,839 | 43,540 | 1.57% | 4,382 | 11 | City |
| Linden | 7 | 46,319 | 43,540 | 1.01% | 4,334 | 11 | City |
| Westfield | 8 | 34,022 | 30,898 | 2.98% | 5,060 | 7 | Town |
| Westfield | 9 | 32,626 | 30,898 | 0.89% | 4,852 | 7 | Town |
| Rahway | 10 | 31,685 | 29,671 | 1.48% | 8,133 | 4 | City |
| Rahway | 11 | 31,309 | 29,671 | 0.88% | 8,036 | 4 | City |
| Scotch Plains | 12 | 26,005 | 24,855 | 1.53% | 2,883 | 9 | Township |
| Cranford | 13 | 25,285 | 23,815 | 1.55% | 5,230 | 5 | Township |
| Summit | 14 | 23,884 | 22,639 | 1.66% | 3,985 | 6 | City |
| Roselle | 15 | 23,776 | 22,606 | 1.52% | 9,023 | 3 | Borough |
| Hillside | 16 | 23,370 | 22,342 | 1.48% | 8,446 | 3 | Township |
| Summit | 17 | 23,333 | 22,639 | 0.5% | 3,893 | 6 | City |
| Roselle | 18 | 23,293 | 22,606 | 0.5% | 8,840 | 3 | Borough |
| Springfield | 19 | 18,646 | 17,106 | 2.8% | 3,616 | 5 | Township |
| Clark | 20 | 17,481 | 15,464 | 3.57% | 4,091 | 4 | Township |
| Berkeley Heights | 21 | 16,554 | 13,203 | 6.58% | 2,661 | 6 | Township |
| Roselle Park | 22 | 14,844 | 14,005 | 1.55% | 12,118 | 1 | Borough |
| Roselle Park | 23 | 14,582 | 14,005 | 0.66% | 11,904 | 1 | Borough |
| New Providence | 24 | 14,407 | 13,704 | 1.59% | 3,906 | 4 | Borough |
| New Providence | 25 | 14,083 | 13,704 | 0.45% | 3,819 | 4 | Borough |
| Kenilworth | 26 | 8,793 | 8,392 | 1.54% | 4,095 | 2 | Borough |
| Kenilworth | 27 | 8,594 | 8,392 | 0.4% | 4,003 | 2 | Borough |
| Fanwood | 28 | 8,340 | 7,749 | 2.28% | 6,224 | 1 | Borough |
| Fanwood | 29 | 8,077 | 7,749 | 0.69% | 6,028 | 1 | Borough |
| Mountainside | 30 | 7,606 | 6,992 | 2.55% | 1,903 | 4 | Borough |
| Mountainside | 31 | 7,346 | 6,992 | 0.81% | 1,838 | 4 | Borough |
| Union | 32 | 6,806 | 6,495 | 2.02% | 363 | 19 | Township |
| Garwood | 33 | 5,804 | 4,430 | 4.11% | 8,929 | 1 | Borough |
| Garwood | 34 | 5,544 | 4,430 | 1.82% | 8,529 | 1 | Borough |
| Springfield | 35 | 3,355 | 3,239 | 0.93% | 114 | 30 | Township |
| Winfield | 36 | 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 36 cities in Union County, New Jersey.