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.The hamlet has a large community of Orthodox Jews, consisting predominantly of Hasidim, including Vizhnitz Hasidim, who reside mostly in the village of Kaser.