The county board of any county having an assessed valuation, as equalized by the Department of Revenue, of all real property located within the county of at least $300 million but less than $5 billion, or the county boards, acting jointly, of any combination of counties having an assessed valuation, as equalized by the Department of Revenue, of all real property within such combination of counties within the limits established by this Section may by resolution or ordinance provide for the formation of a Metropolitan Exposition, Auditorium and Office Building Authority with the powers, duties, responsibilities and privileges provided in this Article.
     The principal office of the Authority shall be at the site of the Authority’s buildings.