Neb. Rev. Stat. § 16-101: Neb. Rev. Stat. § 16-101

All cities having more than five thousand and not 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 shall be known as cities of the first class. The population of a city of the first class shall consist of the people residing within the territorial boundaries of such city and the residents of any territory duly and properly annexed to such city.