21 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| East Greenbush | 1 | 16,388 | 16,699 | -0.19% | 682 | 24.02 | Town |
| North Greenbush | 2 | 13,318 | 13,289 | 0.25% | 718 | 18.54 | Town |
| Schodack | 3 | 12,826 | 12,943 | -0.11% | 207 | 61.93 | Town |
| Brunswick | 4 | 12,403 | 12,580 | -0.13% | 280 | 44.35 | Town |
| Rensselaer | 5 | 9,375 | 9,212 | 0.35% | 2,949 | 3.18 | City |
| Sand Lake | 6 | 8,290 | 8,338 | 0% | 237 | 35.05 | Town |
| Schaghticoke | 7 | 7,255 | 7,393 | -0.29% | 146 | 49.74 | Town |
| Hoosick | 8 | 6,621 | 6,702 | -0.03% | 105 | 63.03 | Town |
| Pittstown | 9 | 5,393 | 5,525 | -0.35% | 87 | 61.65 | Town |
| Nassau | 10 | 4,455 | 4,541 | -0.22% | 100 | 44.44 | Town |
| Poestenkill | 11 | 4,299 | 4,312 | 0.07% | 133 | 32.35 | Town |
| Hoosick Falls | 12 | 3,115 | 3,204 | -0.57% | 1,949 | 1.60 | Village |
| Stephentown | 13 | 2,740 | 2,785 | -0.26% | 47 | 57.89 | Town |
| Grafton | 14 | 2,096 | 2,052 | 0.58% | 47 | 44.72 | Town |
| Berlin | 15 | 1,793 | 1,808 | 0% | 30 | 59.60 | Town |
| Castleton-on-Hudson | 16 | 1,448 | 1,467 | -0.27% | 2,028 | 0.71 | Village |
| Petersburgh | 17 | 1,367 | 1,374 | 0.07% | 33 | 41.61 | Town |
| Nassau | 18 | 1,067 | 1,102 | -0.65% | 1,526 | 0.70 | Village |
| Schaghticoke | 19 | 543 | 558 | -0.55% | 716 | 0.76 | Village |
| East Nassau | 20 | 508 | 522 | -0.59% | 104 | 4.86 | Village |
| Valley Falls | 21 | 445 | 457 | -0.45% | 961 | 0.46 | Village |
East Greenbush is the largest city in Rensselaer County, with a population of 16,388.
Valley Falls is the smallest city in Rensselaer County.
There are 21 cities in Rensselaer County, New York.