Hillside Lake is a hamlet and census-designated place (CDP) in Dutchess County, New York, United States. As of the 2020 census, Hillside Lake had a population of 1,091. It is part of the Kiryas Joel–Poughkeepsie–Newburgh, NY Metropolitan Statistical Area as well as the larger New York–Newark–Bridgeport, NY-NJ-CT-PA Combined Statistical Area.