Drag,
Please confirm anything I say for yourself. Any information I give you here could be outdated/inaccurate, especially considering that local ordinances can vary in Illinois.
Illinois state law is based upon intent. If you have no intent to use the knife against another person illegally (I don't, I'll assume you don't either) then the law as it is currently written allows you to carry a hunting knife. If you intend to use a weapon illegally, then even a broken bottle is considered an illegal weapon. As of my last information, there are no blade length restrictions - it just has to be a "hunting knife". Now, what contitutes a hunting knife? It can't be a dagger, bowie, stiletto, etc....you get the picture. Personally, I like my Spyderco Endura for hunting and fishing. I'm thinking of the Cold Steel Master Hunter since I really like carrying fized blade knives.
Chicago is a whole, 'nother story. I believe the Chicago limit is 2 1/2 or 3" with exception given to emergency personnel and tradesman who carry knives for their trade and are working within the city (i.e. carpet layers knives). I carry the Spyderco outside Chicago and a crkt peck in the city.
Tim