720 ILCS 5/24-5

(a) Any person who shall knowingly or intentionally change, alter, remove or obliterate the name of the importer's or manufacturer's serial number of any firearm commits a Class 2 felony.

(b) A person who possesses any firearm upon which any such importer's or manufacturer's serial number has been changed, altered, removed or obliterated commits a Class 3 felony.

(c) Nothing in this Section shall prevent a person from making repairs, replacement of parts, or other changes to a firearm if those repairs, replacement of parts, or changes cause the removal of the name of the maker, model, or other marks of identification other than the serial number on the firearm's frame or receiver.

(d) A prosecution for a violation of this Section may be commenced within 6 years after the commission of the offense.