(a) Any area of contiguous territory having a population of not less than 5,000 and containing one or more municipalities as defined by this Act, and in which there is not included any territory contained within the corporate limits of an existing Airport Authority, and in which there is not included any territory or airport facilities of a municipal corporation having a population of 500,000 or more which owns, maintains, or operates an airport or airports within or without its corporate limits, may be incorporated as an Airport Authority in the manner provided in Sections 2.1 through 2.6 of this Act; provided, however, that nothing herein contained shall prohibit any municipality whose territory lies both inside and outside a county that is incorporated as a Metropolitan Airport Authority with the majority of the territory lying outside the county from exercising the authority to own, maintain, or operate an airport under the provisions of Division 103 of Article 11 of the Illinois Municipal Code.
     (b) The entire territory within the corporate limits of a county with a population greater than 600,000 and less than 3,000,000, and contiguous to a county with a population in excess of 1,000,000 inhabitants, except the territory of any municipality whose territory lies both inside and outside the county with the majority of the territory lying outside the county, shall be incorporated as a Metropolitan Airport Authority in the manner provided in Section 2.7 of this Act.