Wyo. Stat. § 37-13-118
After the public hearing has been concluded and all corrections made to the assessment list, the governing body shall proceed to adopt the assessment resolution. The resolution and supporting findings shall be conclusive against all persons unless an action contesting the validity of this law or the acts contemplated by this law shall be commenced in a court of competent jurisdiction within thirty (30) days after the adoption of the assessment ordinance. Thereafter, any such action shall be barred and the organization of the district, the assessment levied pursuant thereto, or any other act authorized by this statute shall not be directly or collaterally questioned in any suit, action, or proceeding. The statute of limitations provided herein shall be an additional limitation to and supplement any requirements of the Wyoming Administrative Procedure Act or any rules issued thereunder. If the contest is unsuccessful, the court may order the plaintiff to pay the costs thereof, and, in its discretion, may require a bond in a sufficient amount to cover the costs at the commencement of the action. The burden of proof to show that the special assessment or part thereof is invalid, inequitable or unjust shall rest upon the party who brings the suit.
W.S. 37-13-118