Monticello /ˌmɒntɨˈsɛloʊ/ is a village located in Thompson in Sullivan County, New York, United States. The population was 6,726 at the 2010 census. It is the seat for the Town of Thompson and the county seat of Sullivan County. The village was named after the residence of Thomas Jefferson.The Village of Monticello is in the central part of Thompson, adjacent to New York Route 17. Monticello is one of the largest villages in the county.