220 ILCS 5/5-106
Each public utility shall have an office in one of the cities, villages or incorporated towns in this State in which its property or some part thereof is located, and shall keep in said office all such books, accounts, papers, records and memoranda as shall be ordered by the Commission to be kept within the State. The address of such office shall be filed with the Commission. No books, accounts, papers, records or memoranda ordered by the Commission to be kept within the State shall be at any time removed from the State, except upon such conditions as may be prescribed by the Commission.
Each public utility shall be liable for, and upon proper invoice from the Commission shall promptly reimburse the Commission for, the reasonable costs and expenses associated with the audit or inspection of any books, accounts, papers, records and memoranda kept outside the State.
220 ILCS 5/5-106