20 ILCS 1805/83

Whenever there is a tumult, riot, mob or body of persons acting together by force with attempt to commit a felony, or to offer violence to persons or property, or by force or violence to break or resist the laws of the State, or when such tumult, riot or mob is threatened it shall be deemed that a time of public disorder and danger then exists, and it shall be the duty of the Governor thereupon to order such military force as he may deem necessary to aid the civil authorities in suppressing such violence and executing the law.