Monticello ( ) is a city in Piatt County, Illinois, United States. The population was 5,941 at the 2020 census. It is the county seat of Piatt County. Geography Monticello is located at (40.028092, −88.573003). According to the 2010 census, Monticello has a total area of , of which (or 99.24%) is land and (or 0.76%) is water. Monticello is located in East Central Illinois between the cities of Decatur and Champaign, Illinois. Monticello is nearly equidistant from Chicago, St. Louis, and Indianapolis. Landmarks Robert Allerton Park, which belongs to the University of Illinois at Urbana–Champaign and includes 1,500 acres of woodland and prairie areas, a meadow, a conference and retreat center, formal sculpture gardens, hiking trails, lodging facilities, a summer camp location, and a Georgian style mansion, is located just outside Monticello, to the southwest. The Allerton Natural Area within the park was designated a National Natural Landmark in 1970. Monticello Railway Museum is located on the north side of Monticello. The Monticello Railway Museum is a non-profit operating railroad that offers train rides to the public from May to October. History Monticello's first non-native resident was George Hayworth. Hayworth came to the area in 1822 to serve as a U.S. liaison agent to local Native American tribes. Hayworth did not remain, but in 1829, James A. Piatt purchased Hayworth's small log cabin. Soon more settlers arrived. In 1837, residents decided to form a new town. Abraham Marquiss, William Barnes, James McReynolds, and James A. Piatt Jr. formed a joint stock company and purchased land from James A. Piatt. Upon McReynolds' suggestion, the town was christened Monticello – after the home of Thomas Jefferson. Monticello officially became a town on July 1, 1837. Townsfolk held a celebration on July 4. The first house in the new town was built by a Mr. Cass who used the building as his home and a grocery store. The second house was a log cabin built by John Tenbrooke. In 1839, Nicholas DeVore built the "Old Fort" which was later used as a hotel. Monticello continued to grow as the population increased over the next decade. The citizens of Monticello were unhappy with the distance required to travel to the county seat for their legal issues. Due to the petitions of George Patterson and others, a new county was established on January 27, 1841: Piatt County – named in honor the first permanent