Idaho Code § 50-103: Census.

Within 30 days following the proclamation of incorporation, the city council shall request that an official enumeration of the inhabitants of the newly incorporated city be taken by the bureau of census, U.S. department of commerce, for the purpose of ascertaining the population of said city, the results of which shall be certified to the offices of the county clerk and the secretary of state, and which shall then become the official census and be used for the purpose of apportioning any and all state collected moneys to said city until the next regular or subsequent census be taken.