That info is made available in a brochure entitled "Illinois Gun Laws - Common Questions & Answers. Illinois Gun Statutes". It's put out by the Il State Police and Il Dept of Natural Resources.
ISP Media Information 217-782-6637
ISP FOID & Transfer Inquiry 217-782-3310
IDNR Information 217-782-6302
IDNR Law Enforcement Office of IDNR 217-782-6431
Here's the number on the back of the pamphlet tollfree 877-306-8101
The pamphlet is free. I would call and get a copy and keep it when you're passing through Il.
It might save some hassles if you can show that you're complying by showing their own handout to them.
Remember, these laws don't include local ordinances. Some Federal protection is provided, but don't count on it. In other words, stay away from Chicago.
"Illinois Unlawful Use of Weapons does not preempt local ordinances from banning firearms. Persons carrying or transporting firearms through such communities could be subject to local firearm ordinances. Federal law does attempt to provide limited protection in these circumstances, but when transporting firearms in unfamiliar communities, it is a good idea to check with authorities on local law."