430 ILCS 115/7

If any other State has a safety code for mobile structures or modular dwellings at least equal to the codes promulgated by the Department and the Department determines that such safety standards are being enforced by such other state, the Department shall place such other state upon a reciprocity list, which list shall be available to any interested person. Any mobile structures or modular dwelling which bears the seal of any state which has been placed on the reciprocity list, or which bears a seal approved by such state as sufficient evidence of compliance, shall not be required to affix the seal of this state prescribed by Section 4 of this Act.