70 ILCS 1835/31
The Board may investigate conditions in which it has an interest within the area of the District, the enforcement of its ordinances, rules and regulations, and the action, conduct and efficiency of all officers, agents and employees of the District. In the conduct of such investigations the Board may hold public hearings on its own motion, and shall hold public hearings on complaint of any municipality within the District. Each member of the Board shall have power to administer oaths, and the secretary, by order of the Board, shall issue subpoenas to secure the attendance and testimony of witnesses, and the production of books and papers relevant to such investigations and to any hearing before the Board or any member thereof.
Any circuit court of this State, upon application of the Board or any member thereof, may compel the attendance of witnesses, the production of books and papers, and giving of testimony before the Board or before any member thereof or any officer's committee appointed by the Board, by attachment for contempt or otherwise in the same manner as the production of evidence may be compelled before the court.
70 ILCS 1835/31