21 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| East Greenbush | 1 | 16,707 | 16,807 | 0.2% | 696 | 24 | Town |
| North Greenbush | 2 | 13,777 | 13,298 | 1.18% | 743 | 19 | Town |
| Schodack | 3 | 13,066 | 12,948 | 0.42% | 211 | 62 | Town |
| Brunswick | 4 | 12,604 | 12,585 | 0.34% | 284 | 44 | Town |
| Rensselaer | 5 | 9,577 | 9,205 | 0.65% | 3,013 | 3 | City |
| Sand Lake | 6 | 8,425 | 8,336 | 0.43% | 240 | 35 | Town |
| Schaghticoke | 7 | 7,380 | 7,396 | 0.27% | 148 | 50 | Town |
| Hoosick | 8 | 6,800 | 6,702 | 0.77% | 108 | 63 | Town |
| Pittstown | 9 | 5,473 | 5,527 | 0.2% | 89 | 62 | Town |
| Nassau | 10 | 4,536 | 4,543 | 0.29% | 102 | 44 | Town |
| Poestenkill | 11 | 4,443 | 4,313 | 1.02% | 137 | 32 | Town |
| Hoosick Falls | 12 | 3,184 | 3,202 | -0.09% | 1,992 | 2 | Village |
| Stephentown | 13 | 2,813 | 2,788 | 0.54% | 49 | 58 | Town |
| Grafton | 14 | 2,128 | 2,053 | 0.76% | 48 | 45 | Town |
| Berlin | 15 | 1,724 | 1,702 | 0.7% | 29 | 60 | Town |
| Castleton-on-Hudson | 16 | 1,470 | 1,472 | 0% | 2,059 | 1 | Village |
| Petersburgh | 17 | 1,389 | 1,374 | 0.43% | 33 | 42 | Town |
| Nassau | 18 | 1,084 | 1,105 | -0.28% | 1,551 | 1 | Village |
| Schaghticoke | 19 | 547 | 559 | -0.36% | 722 | 1 | Village |
| East Nassau | 20 | 513 | 521 | -0.19% | 105 | 5 | Village |
| Valley Falls | 21 | 450 | 458 | -0.22% | 972 | 0 | Village |
East Greenbush is the largest city in Rensselaer County, with a population of 16,707.
Valley Falls is the smallest city in Rensselaer County, with a population of 450.
There are 21 cities in Rensselaer County, New York.