Note: As defined by the US Census Bureau, a city's official boundaries often extend miles beyond the city itself and may even cross county lines. As such, several thousand US cities officially exist in two or more counties (and therefore appear on multiple counties' lists of cities.)
City | Rank | 2024 Pop. | 2020 Pop. | Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| East Greenbush | 1 | 16,420 | 16,699 | -0.19% | 684 | 24.0 | Town |
| North Greenbush | 2 | 13,285 | 13,289 | 0.25% | 717 | 18.5 | Town |
| Schodack | 3 | 12,840 | 12,943 | -0.11% | 207 | 61.9 | Town |
| Brunswick | 4 | 12,419 | 12,580 | -0.13% | 280 | 44.4 | Town |
| Rensselaer | 5 | 9,342 | 9,212 | 0.34% | 2,939 | 3.2 | City |
| Sand Lake | 6 | 8,290 | 8,338 | 0% | 237 | 35.0 | Town |
| Schaghticoke | 7 | 7,276 | 7,393 | -0.29% | 146 | 49.7 | Town |
| Hoosick | 8 | 6,623 | 6,702 | -0.03% | 105 | 63.0 | Town |
| Pittstown | 9 | 5,412 | 5,525 | -0.35% | 88 | 61.6 | Town |
| Nassau | 10 | 4,465 | 4,541 | -0.22% | 100 | 44.4 | Town |
| Poestenkill | 11 | 4,296 | 4,312 | 0.07% | 133 | 32.4 | Town |
| Hoosick Falls | 12 | 3,133 | 3,204 | -0.57% | 1,961 | 1.6 | Village |
| Stephentown | 13 | 2,747 | 2,785 | -0.25% | 47 | 57.9 | Town |
| Grafton | 14 | 2,084 | 2,052 | 0.58% | 47 | 44.7 | Town |
| Berlin | 15 | 1,793 | 1,808 | 0% | 30 | 59.6 | Town |
| Castleton-on-Hudson | 16 | 1,452 | 1,467 | -0.27% | 2,034 | 0.7 | Village |
| Petersburgh | 17 | 1,366 | 1,374 | 0.07% | 33 | 41.6 | Town |
| Nassau | 18 | 1,074 | 1,102 | -0.65% | 1,536 | 0.7 | Village |
| Schaghticoke | 19 | 546 | 558 | -0.55% | 720 | 0.8 | Village |
| East Nassau | 20 | 511 | 522 | -0.58% | 105 | 4.9 | Village |
| Valley Falls | 21 | 447 | 457 | -0.67% | 965 | 0.5 | Village |
Note: City markers shown outside the county boundary mean that a part of the city extends into this county, but is primarily located in an adjacent county.
East Greenbush is the largest city in Rensselaer County.
Valley Falls is the smallest city in Rensselaer County.
There are 21 cities in Rensselaer County, New York.