Cahokia Mounds State Historic Site is located near Collinsville, Illinois, and is the largest pre-Columbian settlement north of Mexico. It features a series of earthen mounds built by the Mississippian culture between 600 and 1400 AD. The site includes the famous Monks Mound, which is the largest mound in North America and served as a ceremonial center. Designated a UNESCO World Heritage Site in 1982, Cahokia Mounds covers over 2,200 acres and contains around 80 mounds. The site provides insight into the social, political, and economic life of the Cahokia people, who were known for their advanced agricultural practices and complex societal structures.