625 ILCS 5/18c-2104

The rules of evidence which apply in civil cases before the circuit courts of this State shall, except as otherwise provided herein, apply to proceedings before the Commission under this Chapter. Evidence not admissible under the rules of evidence applicable in civil courts may be admitted if it is of a type commonly relied upon by prudent persons in the conduct of their affairs. Objections must be made at hearing to preserve them on appeal. Evidence may be received orally or in writing.