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).
Boundaries
The Illinois Territory originally included lands that became the states of Illinois, Wisconsin, the eastern portion of Minnesota, and the western portion of the upper peninsula of Michigan. As Illinois was preparing to become a state, the remaining area of the territory was attached to the Michigan Territory.
The original boundaries of the Territory were defined as follows:
"...all that part of the Indiana Territory which lies west of the Wabash river, and a direct line drawn from the said Wabash river and Post Vincennes, due north to the territorial line between the United States and Canada..."
Kaskaskia was the territorial capital. The 1810 census showed a population of 12,282.[2]
In 1818, the southern half of the territory was admitted to the United States as the State of Illinois. The northern half, modern Wisconsin and parts of modern Minnesota and Michigan became part of the Territory of Michigan.
^Heidler, David Stephen; Heidler, Jeanne T., eds. (2004). "Illinois Territory". Encyclopedia of the War of 1812. Naval Institute Press. ISBN978-1591143628. Retrieved March 10, 2009.