The Ilinoue [Illinois], the Kakachkiouek [Kaskaskia], [and] Peoualen [Peoria] . . . dwell on The Banks of the Missisipi, and all speak the same Language. (Claude Dablon, 1673) Contraction of Illinois Indian territory, 1650-1832 enlarge

At the time of initial European contact, the territory of the Illinois, which the French called the "Illinois Country," consisted of a large triangular section of the central Mississippi River valley. The Peoria, Moingwena, and several other Illinois tribes occupied the northwestern part of the region in what is now eastern Iowa; the Kaskaskia were settled to the northeast in the upper Illinois River valley; the Cahokia and Tamaroa occupied the central part of the region in western Illinois and eastern Missouri; and the Michigamea lived in northeastern Arkansas. The Illinois' territory shrank dramatically during the 1700s and early 1800s as their population declined because of warfare and disease.