Rensselaer is a city in Rensselaer County, New York, United States, and is located on the Hudson River directly opposite Albany. As of the 2010 census, the city population was 9,392; in 1920, it was 10,832. The name is from Kiliaen van Rensselaer, the original landowner of the region in New Netherland. Rensselaer is on the west border of the county. Earliest settlement occurred as early as 1628.