27 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| East Greenbush | 1 | 16,388 | 16,699 | -0.19% | 682 | 24 | Town |
| North Greenbush | 2 | 13,318 | 13,289 | 0.25% | 718 | 19 | Town |
| Schodack | 3 | 12,826 | 12,943 | -0.11% | 207 | 62 | Town |
| Brunswick | 4 | 12,403 | 12,580 | -0.13% | 280 | 44 | Town |
| Rensselaer | 5 | 9,375 | 9,212 | 0.35% | 2,949 | 3 | City |
| Sand Lake | 6 | 8,290 | 8,338 | 0% | 237 | 35 | Town |
| Schaghticoke | 7 | 7,255 | 7,393 | -0.29% | 146 | 50 | Town |
| East Greenbush | 8 | 7,092 | 6,299 | 2.52% | 1,811 | 4 | CDP |
| Hoosick | 9 | 6,621 | 6,702 | -0.03% | 105 | 63 | Town |
| Hampton Manor | 10 | 6,076 | 5,161 | 4.18% | 2,027 | 3 | CDP |
| Pittstown | 11 | 5,393 | 5,525 | -0.35% | 87 | 62 | Town |
| Nassau | 12 | 4,455 | 4,541 | -0.22% | 100 | 44 | Town |
| Poestenkill | 13 | 4,299 | 4,312 | 0.07% | 133 | 32 | Town |
| Wynantskill | 14 | 3,785 | 3,420 | 0.91% | 1,107 | 3 | CDP |
| West Sand Lake | 15 | 3,465 | 3,391 | 1.58% | 727 | 5 | CDP |
| Hoosick Falls | 16 | 3,115 | 3,204 | -0.57% | 1,949 | 2 | Village |
| Stephentown | 17 | 2,740 | 2,785 | -0.25% | 47 | 58 | Town |
| Grafton | 18 | 2,096 | 2,052 | 0.58% | 47 | 45 | Town |
| Berlin | 19 | 1,793 | 1,808 | 0% | 30 | 60 | Town |
| Averill Park | 20 | 1,587 | 1,466 | -0.44% | 393 | 4 | CDP |
| Castleton-on-Hudson | 21 | 1,448 | 1,467 | -0.28% | 2,028 | 1 | Village |
| Petersburgh | 22 | 1,367 | 1,374 | 0.07% | 33 | 42 | Town |
| Nassau | 23 | 1,067 | 1,102 | -0.65% | 1,526 | 1 | Village |
| Poestenkill | 24 | 677 | 814 | -3.7% | 115 | 6 | CDP |
| Schaghticoke | 25 | 543 | 558 | -0.55% | 716 | 1 | Village |
| East Nassau | 26 | 508 | 522 | -0.59% | 104 | 5 | Village |
| Valley Falls | 27 | 445 | 457 | -0.45% | 961 | 0 | 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, with a population of 445.
There are 27 cities in Rensselaer County, New York.