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 completely surrounded by the hamlet of Monsey. The 2010 census listed the population at 18,412. Rockland County was inhabited by the Munsee band of Lenape Native Americans, who were speakers of the Algonquian languages. Monsey Glen, an Indian encampment, is located west of the intersection of State Route 59 and State Route 306.