65 ILCS 90/15

If a zone is established, an authorized representative of the municipality, upon presentation of his or her credentials, shall have the authority to enter at all reasonable times to any premises on which a water pollution, waste, or contamination source, including, but not limited to, septic tanks, is located for the purpose of inspection, rehabilitation or maintenance of such source, including securing samples of discharges therefrom, or any records required to be maintained in connection therewith by federal, State, or local law, order, regulation or rule.