About 1000 A.D., people of the Mississippian culture began to spread northwestward from their center at Cahokia into present-day Fulton County.

Of the culture they represented for the next 300 year present-day archaeologists have discovered several thousand mound and village sites in Fulton County alone as well as eight central towns along the Illinois River starting at Peoria and equally spaced downstream for 80 miles.

Small in comparison to Mississippian centers in Southern Illinois the towns usually had only a single platform mound and a central plaza surrounded by an occupational area. They covered an average of 10 to 15 acres.

The Mississippian culture people crowded in with what is known as the late Woodland cultural group in the more attractive town sites but the two lived in relative harmony. The people dwelled in small earthern houses, some of which were clearly devoted to religious purposes. Objects found at the confluence of the Spoon and Illinois rivers indicate that trade provided continued contacts Cahokia, which greatly influenced the hunting/farming-based culture of the northern settlement.

Most famous of the sites is Dickson Mounds, a burial place established around 1000 A.D. with peak usage between 1100 and 1250 A.D. and few burials after 1300 A.D. The Dickson Cemetery Mound is located about three miles southeast of Lewistown on the eastern edge of the region of gently rolling plains and high on a point of the Illinois River bluff, more than 90 feet above the valley floor, providing a beautiful view of the Illinois and Spoon river valleys to the east and the south.

The end of three centuries of prehistoric activity at Dickson coincided with the decline of Cahokia. It remains unknown if collapse was due to religious or political change, warfare, major climatic shift, or disease. Recent speculation is that the Cahokia people who founded the Dickson settlement eventually brought plague to the area, for the final burials in the Dickson Cemetery Mound included large numbers of mass graves. Shortly afterwards newcomers from the Oneota culture arrived and attracted the remnants of the population. But in a few generations they too were gone, leaving the area a cultural void.

William Dickson who migrated from Kentucky in the late 1830s and settled the land that included Dickson Mounds discovered human bones when preparing the land for an orchard in the 1860s. Don Dickson of the same family made the first scientific excavation in the late 1920s, exposing more than 200 burial sites in the following years. The family constructed a small building over the main site soon after; but because it was the first place where prehistoric materials were left in place for viewing, tourist traffic became a problem.

The site was sold to the state of Illinois in 1945. It exists as a reminder that the Illinois plains supported life and culture for many hundreds of years before Europeans arrived.