65 ILCS 5/9-3-34

No litigation, suit or proceeding of any kind or character shall be instituted touching the sufficiency of the plans, specifications, estimate of the cost, or ordinance authorizing the improvement, unless such litigation, suit or proceeding is instituted within 15 days after the adoption of the ordinance by the corporate authorities of such municipality authorizing and directing the improvement to be made. No litigation, suit or proceeding of any kind or character shall be instituted to collaterally attack the final acceptance of the work by the corporate authorities unless such litigation, suit or proceeding is instituted within 15 days after the final acceptance of the work by the corporate authorities.