Cahokia is a large Mississippian (AD 1000-1600) agricultural settlement and mound group located on the American Bottom of the Mississippi River in Illinois. At its height, Cahokia was the center of the Mississippian culture, with a population of about 20,000 people and trade connections throughout the midwest.
Many of Cahokia's outlying settlements in the vicinity of East St. Louis were investigated in advance of highway construction. The researcher most associated with Cahokia would probably be Melvin L. Fowler, who conducted excavations in the 1960s and 1970s. Recent investigations are ongoing field schools from Southern Illinois University at Edwardsville.
Cahokia is a state park in Illinois and open to visitors, and they have an excellent interpretive center to help you understand what was going on so long ago.
Sources and More Information
This article is a part of the About.com Guide to Mississippian Period, and part of the Dictionary of Archaeology.
I've put together an extensive bibliography on Cahokia if you're interested in reading in depth. If you have GoogleEarth installed on your computer, JQ Jacobs has a placemarker for Cahokia Mounds established so you can get a great aerial view and find some more info as well.
Finally, Mary Harrsch has several photographs from Cahokia and the Interpretive Center there in her collection called The Moundbuilders.
