Neb. Rev. Stat. § 15-102: Neb. Rev. Stat. § 15-102

Whenever any city of the first class attains a population of more than one hundred thousand inhabitants as determined by the most recent federal decennial census or the most recent revised certified count by the United States Bureau of the Census, 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 primary class.