70 ILCS 605/4-22
Notice of the hearing on the petition, unless other notice is directed by the court as provided in Section 4-21, shall be given by publishing the notice in a newspaper of general circulation published in the county in which the district is situated. The notice shall be published once each week for 2 successive weeks. The first publication of the notice shall be at least 3 weeks prior to the date fixed for hearing. When the district is situated in 2 or more counties, then such notice shall be given as aforesaid by publishing the same in a newspaper of general circulation published in each of said counties. If no newspaper of general circulation is published in any such county, then publication of the notice shall be in a newspaper having general circulation in that county.
The petition shall be accompanied by the affidavit of one or more credible persons giving the names and addresses of all the owners of land situated in the district, if known, or, if unknown, the names and addresses of the persons who last paid the general taxes on the land for which the names or addresses of the owners are unknown, as shown by the collector's books in the county in which such land is situated. The petitioners or the clerk of the court shall, within 4 days after the first publication of the notice, mail a copy thereof to each person named in the affidavit at the address therein set forth.
The notice given by mail shall be sent first-class, with the postage thereon fully prepaid. The certificate of the clerk or the affidavit of any other credible person, affixed to a copy of the notice, shall be sufficient evidence of the mailing of the notices.
70 ILCS 605/4-22