Illinois is the way the early French explorers/missionaries wrote hilinawe, which simply means “man” in the applicable Indian tongue. I didn’t know there were any derogatory connotations there. “Corruption on the Prairie” might require about sixteen syllables in Algonquin — these supposedly benighted tribes apparently had very little problem with that and wouldn’t have a short word for it. (Now killing raids upon their Indian neighbors, that would be another story. But hey, all men have weaknesses.)
"Man" could mean "guy", like "I know a guy", or "go see my guy", or even "wise guy", or more on poiunt: "MAN this place is messed up!".
Like many politicians in Illinois "Chief Illiniwek" seems to have been a ficticious figure invented out of whole cloth.
Thanks for the linguistic insights.