Monsey is a hamlet and census-designated place in the town of Ramapo, Rockland County, New York, United States, located north of Airmont, east of Viola, south of New Hempstead, and west of Spring Valley. The village of Kaser is surrounded by the hamlet of Monsey. The 2020 census listed the population at 26,954; a 46% increase since the 2010 census.