705 ILCS 15/8

After the completion of the building herein specified, it shall be devoted to the uses of the Department of Justice of the State of Illinois, and be occupied by the Supreme Court, the Attorney General, with his assistants, the State law library, the Appellate Court for the Fourth Judicial District, and the other branches of the Department of Justice of the State now existing or which may hereafter be created.

The care, custody and control of the building, when completed, shall be vested in the Supreme Court.