Wyo. Stat. § 15-1-408
The annexation of any territory is effective upon publication of the ordinance, unless another date is specified in the ordinance. The effective date of the annexation ordinance shall not be less than twenty (20) business days after the public hearing required by W.S. 15-1-405(a). For purposes of real and personal property taxation, the annexation is not effective until January 1 next following the effective date of the ordinance. If an appeal is filed and perfected by a person other than a utility, the effective date is January 1 next following the court's final decision of the matter. If an appeal of the franchise decision is filed and perfected by a utility, the annexation is effective upon the publication of the ordinance unless another date is specified in the ordinance, but the appealing utility shall be permitted to continue its present service in the annexed area until the court's final decision of the matter.
W.S. 15-1-408