Rensselaer County ren-sə-LEER 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.