Monticello is a rural village in, and county seat of, Lewis County, Missouri, United States, along the North Fabius River. The population was 104 at the 2020 census, and according to this census, Monticello is the county seat with the smallest population in the State of Missouri. The town is named in honor of President Thomas Jefferson's estate in Virginia. Monticello is part of the Quincy, IL–MO Micropolitan Statistical Area.