70 ILCS 1830/37
Regular meetings of the Board shall be held at least once in each calendar month, the time and place of meetings to be fixed by the Board. Eight members of the Board constitute a quorum for the transaction of business. All action of the Board shall be by ordinance or resolution. The affirmative vote of at least 7 members shall be necessary for the adoption of any ordinance or resolution. All ordinances and resolutions before taking effect shall be approved and signed by the chairman of the Board, those he does not approve he shall return to the Board with his objections thereto in writing at the next regular meeting of the Board after the passage thereof. If the chairman fails to return any ordinance or resolution with his objections thereto by the time stated, the ordinance or resolution shall take effect without signature. Upon the return of any ordinance or resolution by the chairman with his objections, the vote by which the same was passed shall be reconsidered by the Board. Upon reconsideration if such ordinance or resolution is passed again by the affirmative vote of at least 8 members, it shall go into effect notwithstanding veto by the chairman.
70 ILCS 1830/37