Note: As defined by the US Census Bureau, a city's official boundaries often extend miles beyond the city itself and may even cross county lines. As such, several thousand US cities officially exist in two or more counties (and therefore appear on multiple counties' lists of cities.)
City | Rank | 2024 Pop. | 2020 Pop. | Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Elizabeth | 1 | 136,613 | 136,677 | 0.58% | 11,090 | 12.3 | City |
| Union township | 2 | 60,805 | 59,826 | 0.21% | 6,718 | 9.1 | Township |
| Plainfield | 3 | 54,839 | 54,340 | 0.31% | 9,203 | 6.0 | City |
| Linden | 4 | 44,597 | 43,540 | 1.47% | 4,173 | 10.7 | City |
| Westfield | 5 | 30,535 | 30,895 | -0.08% | 4,541 | 6.7 | Town |
| Rahway | 6 | 29,956 | 29,671 | 0.48% | 7,689 | 3.9 | City |
| Scotch Plains township | 7 | 24,387 | 24,852 | -0.18% | 2,703 | 9.0 | Township |
| Cranford township | 8 | 23,719 | 23,817 | -0.09% | 4,906 | 4.8 | Township |
| Roselle borough | 9 | 22,376 | 22,604 | 0.15% | 8,492 | 2.6 | Borough |
| Summit | 10 | 22,367 | 22,638 | 0.1% | 3,732 | 6.0 | City |
| Hillside township | 11 | 21,965 | 22,344 | -0.12% | 7,938 | 2.8 | Township |
| Springfield township | 12 | 16,834 | 17,106 | -0.07% | 3,264 | 5.2 | Township |
| Clark township | 13 | 15,617 | 15,472 | 1.21% | 3,655 | 4.3 | Township |
| Roselle Park borough | 14 | 13,913 | 14,002 | -0.14% | 11,358 | 1.2 | Borough |
| Berkeley Heights township | 15 | 13,526 | 13,223 | 1.75% | 2,175 | 6.2 | Township |
| New Providence borough | 16 | 13,465 | 13,680 | -0.17% | 3,651 | 3.7 | Borough |
| Kenilworth borough | 17 | 8,248 | 8,393 | -0.13% | 3,842 | 2.1 | Borough |
| Fanwood borough | 18 | 7,657 | 7,748 | 0.03% | 5,714 | 1.3 | Borough |
| Mountainside borough | 19 | 6,911 | 6,988 | -0.19% | 1,729 | 4.0 | Borough |
| Union township | 20 | 6,440 | 6,494 | 0.77% | 343 | 18.8 | Township |
| Garwood borough | 21 | 5,315 | 4,429 | 2.98% | 8,177 | 0.7 | Borough |
| Springfield township | 22 | 3,257 | 3,238 | 0.18% | 110 | 29.5 | Township |
| Winfield township | 23 | 1,390 | 1,415 | -0.14% | 7,680 | 0.2 | Township |
Note: City markers shown outside the county boundary mean that a part of the city extends into this county, but is primarily located in an adjacent county.
Elizabeth is the largest city in Union County.
Winfield township is the smallest city in Union County.
There are 23 cities in Union County, New Jersey.