I have lived most of my life in Wisconsin and Iowa and brown recluse bites are rare enough that if someone gets bitten and develops necrosis then it usually makes the news. While it does happen on rare occasion the chances are extremely low. I heard much more about people being bit by black widows when I lived in California than I ever have about brown recluse bites. Maybe the spiders all like Illinois though and don't cross the border, but if that's true then it shouldn't be that hard to find some evidence to support the claim that they are a common occurance there.
I do know that. 



