55 ILCS 5/5-1057.5

(a) For purposes of this Section, "milkweed" means Asclepias syriaca or other native Asclepias species. (b) A county may not classify milkweed as a noxious or exotic weed. (c) A county may not classify milkweed in a manner inconsistent with this Section. This Section is a limitation under subsection (i) of Section 6 of Article VII of the Illinois Constitution on the concurrent exercise by home rule units of powers and functions exercised by the State.