225 ILCS 440/3.14

For purposes of this Act, "urban area" means an urbanized area or, in the case of an urbanized area encompassing more than one state, that part of the urbanized area in each such state, or an urban place as designated by the Bureau of the Census of the United States having a population of 5,000 or more and not within any urbanized area, within boundaries to be fixed by responsible state and local officials in cooperation with each other, subject to approval by the Secretary of the United States Department of Transportation. Such boundaries shall, as a minimum, encompass the entire urban place designated by the Bureau of the Census.