The county hasn't banned anything, but some towns ban them, or at least tried. Deerfield and Highland Park come to mind, but there may be others, and I don't know the legal status of those without doing more googling. If you can specify the town, it would help.
If you're selling from MI to someone in IL, any firearm will need to go through an FFL here in the state. There's not a common border (guess that big lake doesn't count).
Good summary here (not official, and I'm not affiliated with it):
https://www.alphakoncepts.com/blog/can-an-illinois-resident-buy-a-gun-in-another-state/Edit to add: Magazines don't need to go through the FFL, but any local ordinance might prohibit them as well.
Also, IL has the FOID card system, so there's a portal for people conducting private transactions to check someone's FOID status, but I don't know if out-of-state sellers are obligated to check it. You're also supposed to honor IL's 72-hour waiting period for all firearms.
Someone please correct any of that if I'm wrong!