18 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Bridgewater township | 1 | 45,418 | 45,870 | -0.43% | 1,424 | 31.89 | Township |
| Hillsborough township | 2 | 44,953 | 43,233 | 0.92% | 823 | 54.62 | Township |
| Bernards township | 3 | 28,498 | 27,765 | 0.7% | 1,178 | 24.20 | Township |
| Raritan township | 4 | 25,229 | 23,529 | 1.19% | 673 | 37.48 | Township |
| Montgomery township | 5 | 23,991 | 23,635 | 0.57% | 743 | 32.30 | Township |
| North Plainfield borough | 6 | 22,430 | 22,748 | -0.3% | 7,991 | 2.81 | Borough |
| Warren township | 7 | 16,609 | 15,884 | 1.39% | 849 | 19.57 | Township |
| Branchburg township | 8 | 16,012 | 14,899 | 2.45% | 798 | 20.07 | Township |
| Somerville borough | 9 | 15,612 | 12,359 | 5.05% | 6,678 | 2.34 | Borough |
| Bound Brook borough | 10 | 13,203 | 11,954 | 3.25% | 7,949 | 1.66 | Borough |
| Manville borough | 11 | 10,657 | 10,932 | -0.57% | 4,514 | 2.36 | Borough |
| Raritan borough | 12 | 8,362 | 7,820 | -0.36% | 4,198 | 1.99 | Borough |
| Bedminster township | 13 | 8,133 | 8,250 | -0.28% | 311 | 26.12 | Township |
| Bernardsville borough | 14 | 7,797 | 7,881 | -0.26% | 607 | 12.84 | Borough |
| Green Brook township | 15 | 7,243 | 7,259 | -0.33% | 1,644 | 4.41 | Township |
| Watchung borough | 16 | 6,422 | 6,437 | -0.09% | 1,067 | 6.02 | Borough |
| South Bound Brook borough | 17 | 4,769 | 4,851 | -0.44% | 7,394 | 0.65 | Borough |
| Peapack and Gladstone borough | 18 | 2,508 | 2,552 | -0.6% | 437 | 5.73 | Borough |
Bridgewater township is the largest city in Somerset County, with a population of 45,418.
Peapack and Gladstone borough is the smallest city in Somerset County.
There are 18 cities in Somerset County, New Jersey.