There is no blade length limit in Illinois. Their knife laws make sense ... use a longer blade while committing a crime and you have committed the crime while carrying a "deadly weapon", otherwise, carry away.
I EDC the mini-RSK, not because of what others might say/think, but because its size is better suited to my EDC needs. Heck, even the mini has gotten a comment or two, but I don't worry about it.
I also have the fullsize RSK, and use it when in the field.
I ordered the fullsize M2 RSK, and plan to use it, not keep it a a clean collectable.
Ken K.