Whenever notice is required to be given under the provisions of this Act, a notice published at least twice, with an interval of at least seven (7) days between the two (2) publication dates, in one or two newspapers of general circulation published within the area; or, if any such newspaper is not published within such area, then by publication in at least one newspaper published outside the area but having general circulation in such area and by posting copies of such notice in at least three (3) conspicuous places within the area, such posting to include posting at public places where it may be customary to post notices generally, shall be deemed "due notice."
70 ILCS 405/31