Poestenkill is a town in Rensselaer County, New York, United States. The population was 4,322 at the 2020 census. The town is southeast of Troy and is centrally located in the county.

Rensselaer County is a county in the U.S. state of New York. As of the 2020 census, the population was 161,130. Its county seat is Troy. The county is named in honor of the family of Kiliaen van Rensselaer, the original Dutch owner of the land in the area. The county is part of the Capital District region of the state.