13 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Hamilton township | 1 | 92,050 | 92,057 | 0.22% | 2,333 | 39.45 | Township |
| Trenton | 2 | 89,790 | 90,592 | 0.1% | 11,805 | 7.61 | City |
| Ewing township | 3 | 34,937 | 37,239 | 0.26% | 2,297 | 15.21 | Township |
| Lawrence township | 4 | 31,791 | 33,047 | 0.03% | 1,463 | 21.73 | Township |
| West Windsor township | 5 | 31,449 | 29,529 | 1.52% | 1,231 | 25.55 | Township |
| Princeton | 6 | 30,255 | 30,610 | -0.06% | 1,686 | 17.95 | Township |
| East Windsor township | 7 | 29,748 | 29,937 | -0.02% | 1,911 | 15.57 | Township |
| Hopewell township | 8 | 17,365 | 17,442 | -0.05% | 299 | 58.07 | Township |
| Robbinsville township | 9 | 15,431 | 15,435 | 0.23% | 755 | 20.44 | Township |
| Hightstown borough | 10 | 5,855 | 5,883 | 0.02% | 4,749 | 1.23 | Borough |
| Hopewell township | 11 | 4,363 | 4,377 | 0.11% | 146 | 29.89 | Township |
| Pennington borough | 12 | 2,890 | 2,796 | 0.87% | 3,007 | 0.96 | Borough |
| Hopewell borough | 13 | 1,894 | 1,899 | 0% | 2,616 | 0.72 | Borough |
Hamilton township is the largest city in Mercer County, with a population of 92,050.
Hopewell borough is the smallest city in Mercer County.
There are 13 cities in Mercer County, New Jersey.