Monticello is a village located in Thompson, Sullivan County, within the Catskills region of New York, United States. It is the seat for the town of Thompson, and the county seat of Sullivan County. The population was 7,173 at the 2020 census. The village was named after the residence of Thomas Jefferson. The village is located in the central part of Thompson, adjacent to New York Route 17 and 17B. Monticello is the largest village in the county in both population and area.