105 ILCS 5/15-13

At the close of each day's sale the purchasers shall pay or secure the payment of the purchase money. In case of a failure to do so by 10 a. m. the succeeding day, the lot purchased shall again be offered at public sale, on the terms as before. Regardless of whether or not the sale is made the former purchaser shall be required to pay the difference between his bid and the valuation of the lot, and if he fails to make such payment, the county superintendent may forthwith institute a civil action in his name, as superintendent, for the use of the inhabitants of the township where the land lies, for the required sum; and upon making proof, shall be entitled to judgment, with costs of suit which, when collected, shall be added to the principal of the township fund.