70 ILCS 905/11
In counties not under township organization the county commissioners shall be the board of health for each public health district in the county.
Where a public health district, in counties under township organization, consists of a single town, the supervisor, assessor and town clerk of such town shall be members of the board of health for the public health district.
Where a public health district consists of 2 or more adjacent towns, the supervisors of the towns, together with the chairman of the county board shall be members of the board of health for the public health district; provided, that where the public health district consists of 2 towns, and the supervisor of one of such towns is the chairman of the county board, the presiding officer of the county board, with the advice and consent of the county board, shall appoint a qualified voter from one of such towns to serve as a member of the board of health for a term of one year.
A majority of the board shall constitute a quorum for the transaction of business.
70 ILCS 905/11