The portion that was formerly part of the Northwest Territory and which later became the state of Wisconsin was part of the Indiana Territory when this was formed in 1800. In 1809, it became part of the Illinois Territory; then, when Illinois was about to become a state in 1818, this area was joined to the Michigan Territory. Then the Wisconsin Territory was split off from Michigan Territory in 1836 as the state of Michigan prepared for statehood. In 1838, the section of the territory to the west of the Mississippi became the Iowa Territory.