Ind. Code § 36-10-4-26
(c) The validity of a contract may not be subsequently questioned by any person except in an action to enjoin the performance of the contract instituted within fifteen (15) days after the execution of the contract. After that fifteen (15) day period, all proceedings and orders of the board preliminary to the contract are valid, conclusive, and binding upon all persons and are not subject to attack. The amount of the benefits resulting to all property in the city and the special tax shall be levied only for the balance.
[Pre-Local Government Recodification Citations: 19-7-9-10; 19-7-30-20.]
As added by Acts 1981, P.L.309, SEC.111. Amended by P.L.127-2017, SEC.382.