Kaskaskia River

The Kaskaskia River is a tributary of the Mississippi River, approximately 325 miles (523 km) long, in central and southern Illinois in the United States. The second largest river system within Illinois, it drains a rural area of farms, as well as rolling hills along river bottoms of hardwood forests.
In the early 1700s, the French colonial town of Kaskaskia was founded near the mouth of the river. In 1819, Vandalia, some 80 miles up the river in the interior of the then new state of Illinois was chosen as its state capital, which it served as until 1839. Flooding in the late 19th century caused the Mississippi River to flow over and into the lowest reaches of the Kaskaskia taking the former lower Kaskaskia channel as its new course. Subsequently, the remaining lower reaches of the Kaskaskia have been canalized to allow barge traffic.
"Cascasquia" is an alternative, supposedly more French, spelling of "Kaskaskia" that is sometimes encountered. It was named after a clan of the Illiniwek encountered by the early French Jesuits and other settlers. "Okaw River" was an alternative name for the Kaskaskia that persists in place names along the river, including Okawville, and in a major tributary, the West Okaw River.

Source: Wikipedia https://en.wikipedia.org/wiki/Kaskaskia_River