Neb. Rev. Stat. § 16-102: Neb. Rev. Stat. § 16-102

Whenever any city of the second class attains a population of more than five thousand inhabitants as provided by section 16-101 , the mayor of such city shall certify such fact to the Secretary of State who upon the filing of such certificate shall by proclamation declare such city to be a city of the first class. Upon such proclamation being made by the Secretary of State, every officer of such city shall, within thirty days thereafter, qualify and give bond as provided by sections 16-219 , 16-304 , and 16-318 .