We asked this question to the ADA who taught our law and legal issues in the academy. The only statewide mention having to do with blade length involves the differentiation whether the criminal was carrying a "dangerous weapon" while in the commission of a felony as found in the Legislative Intent portion of the Illinois Criminal Code (720 ILCS 5/33A-1). The term "dangerous weapon" includes three categories (because IL legislators get paid by the word)

Category I weapons:

handgun
sawed-off shotgun
sawed-off rifle
any other firearm small enough to be concealed upon the person
semiautomatic firearm
machine gun

Category II weapons include:

any other rifle
shotgun
spring gun
other firearm
stun gun
taser
knife with a blade of at least 3 inches in length
dagger
dirk
switchblade knife
stiletto
axe
hatchet
other deadly or dangerous weapon or instrument of like character.

Category III weapons include:

bludgeon
black-jack    
slungshot
sand-bag
sand-club
metal knuckles
billy
other dangerous weapon of like character.

Of course, as mentioned, local AHJ's may have different laws.

Yep. Illinois Firearm Concealed Carry Act:

(e) Nothing in this Act shall prohibit a non-resident from transporting a concealed firearm within his or her vehicle in Illinois, if the concealed firearm remains within his or her vehicle and the non-resident:
       (1) is not prohibited from owning or possessing a firearm under federal law;
       (2) is eligible to carry a firearm in public under the laws of his or her state or territory of residence, as evidenced by the possession of a concealed carry license or permit issued by his or her state of residence, if applicable; and
       (3) is not in possession of a license under this Act.
   If the non-resident leaves his or her vehicle unattended, he or she shall store the firearm within a locked vehicle or locked container within the vehicle in accordance with subsection (b) of Section 65 of this Act.