Carry legal in Illinois
Carry is legal in Illinois as long as the firearm is unloaded, enclosed in a case, and you have a valid FOID card. If you are a nonresident, then the law is more "iffy." To be honest, I'm not even sure of all of the changes in the law for nonresidents, as I've been focussed on how the law affects us.
The best advice I would give you, and this isn't to be taken as legal advice since I'm not a lawyer, would be to unload and case your firearm, AND make it inaccessible -- best bet being the trunk. It may be perfectly legal to have it on the back seat (unloaded in a case of course) or under the passenger seat, or maybe even on your person, but YOU should consult the Illinois Compiled Statutes yourself to see what the law says.
My personal stance is I exercise my rights to the very extent to which they are recognized by law. I carried legally in Illinois until I was wrongfully arrested and falsely charged with breaking the law. That legal situation is still ongoing, and the only thing that stops me from carrying today is my financial situation (lawyers are expensive) and that fact that the police still have my pistol.
So my advice: try to find the actual laws that affect you as a nonresident and make a decision on what is best for you. Also keep in mind that if you are going through Chicago or Cook County, be EXTRA careful. It is a messy patchwork of local ordinances (counties and cities can have their own ordinances on firearms -- Cook County, Chicago, and many other places even BAN certain types of firearms altogether!) So definitely consider the trunk route and don't even stop if you're going through Chicago or Cook!
I hope this helps. Enjoy your short (the shorter the better) stay in The Sheeple's Republik of Illannoy
I wish we were more hospitable, but gun owners are treated worse than terrorists here. Best of luck.
Shaun Kranish
Founder-Director,
ICarry.org