Koster Site is located in Illinois

The Koster Site is a prehistoric archaeological site located south of Eldred, Illinois. The site includes eleven settlements dating from 5100 B.C. to 1000 A.D. Nine of the settlements were occupied during the Archaic period, while the other two were inhabited during the Woodland period. The soil strata containing the settlement remains are separated by additional layers of soil, making the site exceptionally well-preserved.

• http://en.wikipedia.org/wiki/Koster Site
• Page 209 - Hunt, P., 2007, Ten Discoveries that Rewrote History: Penguin, New York, 226p.