220 ILCS 5/10-104

All hearings before the Commission or any commissioner or administrative law judge shall be held within the county in which the subject matter of the hearing is situated, or if the subject matter of the hearing is situated in more than one county, then at a place or places designated by the Commission, or agreed upon by the parties in interest, within one or more such counties, or at the place which in the judgment of the Commission shall be most convenient to the parties to be heard.