The original northern border of the state of Illinois was the southern tip of Lake Michigan but Nathaniel Pope helped change this:
[T]he shrewd move in 1818 by Nathaniel Pope, the Illinois Territory’s delegate in Congress, to relocate the original proposed boundary from the southern tip of Lake Michigan is regarded as a decisive event in Illinois history…
Pope’s move provided the groundwork for Chicago to become Illinois’ economic juggernaut and literally turned state politics upside-down as the area grew. But it also had the national implication of ensuring Illinois would be a free state at a time of percolating political unrest over slavery…
Congress “wanted to have a water route between the Great Lakes and the Mississippi River for shipping supplies and soldiers if needed, since the Ohio River route could become contested,” said Olson, co-author of a new book “Managing Mississippi and Ohio River Landscapes” that includes a chapter on the northern border.
Along with giving Illinois access to Lake Michigan, Pope’s border modification raised the population nearly to the 40,000 required for statehood, Olson said in an article he co-authored for the Journal of Earth Science and Engineering.
This is interesting history given Illinois’ later connection to Abraham Lincoln and fighting slavery as well as the rapid spread of the Republican Party and its abolitionist priorities when the party was first founded in Wisconsin in the 1850s.
It might even be more intriguing to see how Pope and others thought about the southwestern edge of Lake Michigan. This was not the only point by which people and supplies could be transferred between the Great Lakes and the Mississippi. Indeed, it was not until several treaties, including a few after statehood (see the Treaty of Chicago), and the construction of the Illinois and Michigan Canal (begun in the 1830s and completed in the late 1840s) that Chicago became a candidate for explosive growth. (And grow it did and quickly encompassed an entire region including significant portions of Wisconsin – see Cronon’s Nature’s Metropolis).