Wyo. Stat. § 37-13-128
No special assessment shall be declared void or set aside in consequence of any error or irregularity permitted or appearing in any of the proceedings under this chapter, but any party feeling aggrieved by any special assessment or proceeding may bring a civil action to adjudicate the grievance if the action is commenced prior to the expiration of thirty (30) days after adoption of the assessment ordinance. Every person whose property is subject to the special assessment and who fails to appear during the public hearings on assessments to raise his objection to the tax shall be deemed to have waived all objection to the assessment except the objection that the governing body lacks jurisdiction to levy the tax, which objection must be raised within thirty (30) days after adoption of the assessment ordinance. Whenever any enactment authorizing the issuance of any bonds pursuant to the improvement contemplated is adopted, the resolution shall be published once in a newspaper in which the original notice of hearing was published. For twenty (20) days thereafter, any person whose property has been assessed and any taxpayer in the district may institute litigation for the purpose of questioning or attacking the legality of such bonds. After the expiration of twenty (20) days, all proceedings by the governing body, the bonds to be issued pursuant thereto, and the special assessments from which the bonds are to be paid, shall be final and no suit challenging the legality thereof may be instituted in this state, and no court shall have the authority to inquire into such matters.
W.S. 37-13-128