Since there is no "illegal blade length" here in Illinois, the answer is no. That's why I can carry a 24" long Bowie knife. However, in the eyes of many LEOs who don't know the law, anything over 3" is illegal, so you still have to do what you can to make it "look better". This comes from a misunderstanding of our criminal code. It says a knife with at least a 3" blade is considered a "dangerous weapon". However, simply posessing a "dangerous weapon" is NOT a crime. It only becomes a crime when you carry it "with intent to use same unlawfully against another". If you use it for legitimate purposes and don't threaten anybody with it, you are fine.