105 ILCS 5/15-9

When the petition and affidavits are delivered to the county superintendent, and the requisite number of votes are in favor of a sale, he shall notify the trustees of the township or township land commissioners, who shall immediately divide the land into tracts or lots of such form and quantity as will produce the largest sum of money, and cause a plat thereof to be made with each lot numbered and defined so that its boundaries may be forever ascertained. In subdividing common school lands, no lot shall contain more than 80 acres and the division may be into town or village lots, with roads, streets or alleys between and through them. All such divisions are hereby declared legal and all such roads, streets and alleys are declared to be public highways.