The Cahokia Mounds State Historic Site /kəˈhoʊkiə/ (11 MS 2) is located on the site of a pre-Columbian Native American city (c. 600–1400 AD) situated directly across the Mississippi River from modern St. Louis, Missouri. This historic park lies in southern Illinois between East St. Louis and Collinsville. The park covers 2,200 acres (890 ha), or about 3.5 square miles (9 km2), and contains about 80 mounds, but the ancient city was much larger. In its heyday, Cahokia covered about 6 square miles (16 km2) and included about 120 human-made earthen mounds in a wide range of sizes, shapes, and functions.
Cahokia was the largest and the most influential urban settlement in the Mississippian culture which developed advanced societies across much of what is now the central and southeastern United States, beginning more than 1000 years before European contact. Cahokia's population at its peak in the 13th century, an estimated 40,000, would not be surpassed by any city in the United States until the late 18th century. Today, Cahokia Mounds is considered the largest and most complex archaeological site north of the great pre-Columbian cities in Mexico.
The Cahokia tribe (not to be confused with the unnamed prehistoric inhabitants of the Cahokia Mounds) were an Algonquian speaking Native American tribe and member of the Illinois Confederation. They were originally located in Illinois, Iowa, Missouri, and Arkansas, later removed to Kansas, and finally to present-day Oklahoma.
The Tamaroa were closely related to the Cahokia.
The Cahokia, along with the Michigamea were eventually absorbed by the Kaskaskia and finally the Peoria.