In any event, Jesuit Father Jacques Marquette and French-Canadian explorer Louis Jolliet undertook the journey and became the first Europeans to meet the Illiniwek (and the Kaskaskia in particular) in their own land near present-day Des Moines, Iowa. The land controlled by the Confederation was approximately the same as present-day Illinois.
The fate of the Kaskaskia,and the rest of the Illiniwek/Illinois, was irrevocably tied up with that of France. When the Seven Years War (called the French and Indian War in North America) ended, the Kaskaskia and other Illiniwek tribes were greatly in decline. The original population estimate reported by early French explorers varied from 6 to 20,000+. But at the conclusion of the French and Indian War, the number was a fraction of the original.
The causes of decline are many and varied (See the work of Emily Blasingham, Indiana University, published in Ethnohistory journal). The Illiniwek made war with their French allies against the most formidable native nations: to the east, the Iroquois; to the northwest, the Sioux and the Fox; to the south, the Chickasaw and Cherokee; to the west, the Osage. Add to combat losses the inevitable losses to European diseases, and it is little wonder the Kaskaskia and other Illinois tribes have almost vanished.
The remnant of the Kaskaskia live in Oklahoma under the banner of the Confederated Peoria Tribe of Oklahoma. It is believed that not a single full-blooded Illinois Indian lives today.
The term "Kaskaskia" lives on in Illinois. The Kaskaskia River, whose headwaters are near Champaign in central Illinois, and whose mouth is near Chester, Illinois, still carries the name of this native nation who once settled throughout its estuarial plain. Kaskaskia College is located in Centralia, Illinois, in Marion County. The city of DuQuoin, Illinois, carries the name of Jean Baptiste DuQuoin (sometimes DuQuoigne), a notable Kaskaskia chieftian of their later history.