Poestenkill is a hamlet (and census-designated place) in Rensselaer County, New York, United States.

As of the census[4] of 2000, there were 1,024 people, 396 households, and 291 families residing in the CDP.

There were 426 housing units at an average density of 73.0 per square mile (28.2/km2).

21.5% of all households were made up of individuals, and 10.6% had someone living alone who was 65 years of age or older.

None of the families and 1.2% of the population were living below the poverty line, including no under eighteens and 3.5% of those over 64.