Illinois Territory separated from Indiana Territory
History of the area
The area was earlier known as "Illinois Country" (Pays des Illinois) while under French control, first as part of French Canada and then in its southern region as part of French Louisiana. The British gained authority over the region east of the Mississippi River from the French, with the 1763 Treaty of Paris marking the end of the French and Indian War and of the French North American colony of New France.
During the American Revolutionary War, Colonel George Rogers Clark took possession of the region for Virginia, which established the "County of Illinois" to exercise nominal governance over the area. Virginia later (1784) ceded nearly all of its land claims north of the Ohio River to the Federal government of the United States.
The area became part of the United States' Northwest Territory (from July 13, 1787, until July 4, 1800), and then part of the Indiana Territory. On February 3, 1809, the 10th United States Congress passed legislation establishing the Illinois Territory, after Congress received petitions from residents in the Mississippi River areas complaining of the difficulties of participating in territorial affairs in Indiana Territory. The portions of the Illinois Territory north of what became the State of Illinois were in 1818 annexed to Michigan Territory, and after several administrative arrangements became a part of the Upper Peninsula of Michigan (1837), the State of Wisconsin (1848), and a northern section of the State of Minnesota (1858).