Illinois Territory created from the western Indiana Territory

Background. The Indiana Territory, originally organized in 1800, underwent significant subdivision during the early nineteenth century. Its geographical area decreased substantially when the Michigan Territory was created in 1805 and the Illinois Territory was established in 1809. These partitions reduced the original landmass, leaving the remaining southeastern portion for future statehood.

Enabling Legislation. On February 3, 1809, the 10th United States Congress passed legislation establishing the Illinois Territory. This action followed petitions from residents in the Mississippi River areas who complained about the difficulties of participating in territorial affairs in Indiana. The new territory existed as an organized incorporated territory until its southern portion became a state in 1818.

Demographic Impact. The creation of the Illinois Territory significantly altered the demographic landscape of the region. By 1810, the Indiana Territory's enumerated population reached 24,520, despite the reduction in size caused by the formation of the Michigan and Illinois Territories. The Illinois Territory itself reported a population of 12,282 in the 1810 census.