Monticello is a village located in the Town of Thompson in Sullivan County, New York. The population was 6,512 at the 2000 census. It is the county seat of Sullivan County. The village was named after the residence of Thomas Jefferson, but is pronounced as "mon-tah-sell-oh". The Village of Monticello is in the central part of the town, adjacent to New York Route 17. Monticello is the largest village in the county.