Lots of cities have municipal ordinances that are stricter than state law about all kinds of matters, including gun and knife control. Best knife control resource is here:
http://www.kniferights.org/index.php?option=com_content&task=view&id=282
From that page:
"8. Chicago, IL: It is illegal to carry
concealed a knife with a blade longer than 2.5-inches. Concealed carry of a double-edged knife is prohibited. Automatic (switchblade) and gravity knives are prohibited entirely. "No person shall sell, offer for sale, loan or give to any person 18 years of age or under any type or kind of knife, any blade of which is two inches in length or longer," with no exceptions. However, no person 18 years or under may carry or possess or conceal on or about his person, any knife with a blade two inches or longer in length. It is a mystery how a minor is supposed to get hold of the knife, albeit of limited length, that they are legally allowed to own or carry."