Monticello is a village located in Thompson in Sullivan County, New York, United States. The population was 6,716 at the 2010 census. It is the seat for the Town of Thompson and the county seat of Sullivan County. 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. The Village of Monticello is located in the southern portion of Upstate New York in the Catskill Mountains region. The climate in Monticello is warm to hot in summer and cold in winter the rainfall is high and so is the snowfall. Monticello is set amongst some very pretty countryside and there is plenty for the tourist to do within the countryside round about.