Wisconsin Statutes Municipalities (Ch. 59 to 68) § 62.05. Classes of cities

(1) Cities shall be divided into 4 classes for administration and the exercise of corporate powers as follows:

(2) Population of cities shall be determined by the last federal census, including a special federal census taken of such city, except in newly incorporated cities when a census is taken as provided by law. Cities shall pass from one class to another when such census shows that the change in population so requires, when provisions for any necessary changes in government are duly made, and when a proclamation of the mayor, declaring the fact, is published according to law.