Wyo. Stat. § 15-3-101
If it is ascertained that any city or town has attained a population of more than four thousand (4,000) inhabitants and that fact is certified to the governor by the mayor of the city or town, attested by its seal, the governor, by public proclamation, shall declare the city or town to be a city of the first class. The proclamation shall be published by the city for three (3) consecutive weeks in a newspaper of general circulation in the city. A certified copy of the proclamation shall be recorded in the office of the county clerk of the county in which the city is situated. The record of the proclamation shall be received as evidence of the organization and corporate existence of the city as a city of the first class in any court within the state.
W.S. 15-3-101