5 ILCS 120/1.02
For the purposes of this Act:
"Meeting" means any gathering, whether in person or by video or audio conference, telephone call, electronic means (such as, without limitation, electronic mail, electronic chat, and instant messaging), or other means of contemporaneous interactive communication, of a majority of a quorum of the members of a public body held for the purpose of discussing public business or, for a 5-member public body, a quorum of the members of a public body held for the purpose of discussing public business.
Accordingly, for a 5-member public body, 3 members of the body constitute a quorum and the affirmative vote of 3 members is necessary to adopt any motion, resolution, or ordinance, unless a greater number is otherwise required.
"Public body" includes all legislative, executive, administrative or advisory bodies of the State, counties, townships, cities, villages, incorporated towns, school districts and all other municipal corporations, boards, bureaus, committees or commissions of this State, and any subsidiary bodies of any of the foregoing including but not limited to committees and subcommittees which are supported in whole or in part by tax revenue, or which expend tax revenue, except the General Assembly and committees or commissions thereof. "Public body" includes tourism boards and convention or civic center boards located in counties that are contiguous to the Mississippi River with populations of more than 250,000 but less than 300,000. "Public body" includes the Health Facilities and Services Review Board. "Public body" does not include a child death review team or the Illinois Child Death Review Teams Executive Council established under the Child Death Review Team Act, an ethics commission acting under the State Officials and Employees Ethics Act, a regional youth advisory board or the Statewide Youth Advisory Board established under the Department of Children and Family Services Statewide Youth Advisory Board Act, or the Illinois Independent Tax Tribunal.
5 ILCS 120/1.02