805 ILCS 305/1
Any 2 or more persons duly licensed to practice a profession under the laws of this State may form a professional association, as distinguished from either a partnership or a corporation, by associating themselves for the purpose of rendering professional services or, if the professional services are within the fields of medicine, dentistry and nursing, related professional services and dividing the gains therefrom as stated in articles of association. Except for an association formed for the purpose of rendering professional services within the fields of medicine, dentistry and nursing, no professional association organized pursuant to this Act shall engage in more than one type of professional service. Each of the members of the association shall be licensed to perform the type of professional service or one of the related professional services for which the association is formed.
805 ILCS 305/1