The Illinois Confederation, sometimes referred to as the Illiniwek or Illini, were a group of 12–13 Native American tribes in the upper Mississippi River valley of North America. The tribes were the Kaskaskia, Cahokia, Peoria, Tamaroa, Moingwena, Michigamea, Chepoussa, Chinkoa, Coiracoentanon, Espeminkia, Maroa, and Tapouara. At the time of European contact in the 17th century, they were believed to number over 10,000 people. Most of the Illinois spoke various dialects of the Miami-Illinois language, one of the Algonquian languages family, with the known exception of the Siouan-speaking Michigamea. They occupied a broad inverted triangle from modern-day Iowa to near the shores of Lake Michigan in modern Chicago south to modern Arkansas. By the mid-18th century, only five principal tribes remained—the Cahokia, Kaskaskia, Michigamea, Peoria, and Tamaroa.
The Illinois River and the entire vast Illinois Country are named after the Illinois Confederacy.
Illinois is from a French rendering of ilinwe (pl. iliniwek). Ilinwe is in turn an Odawa language rendering of irenweewa. (The Ottawa were a neighboring tribe, whom the French met first.) irenawaki or "ilenawaki" means the true (irena or ilena) ones (waki) in the Illinois Confederation language but the confederation word for themselves was inoca or inoka (currently of unknown meaning). Unlike the plural form iliniwek, the term illini does not appear to have a historic linguistic connection.