Minnesota Statutes 410.01 Cities, classes. 

  Cities are hereby divided, for legislative purposes, into 

  classes as follows:  

    First class -- Those having more than 100,000 inhabitants provided that once a city is defined 

    to be of the first class, it shall not be reclassified unless its population decreases by 

    25 percent from the census figures which last qualified the city for inclusion in the class;  

   Second class -- Those having more than 20,000 and not more than 100,000 inhabitants;  

   Third class -- Those having more than 10,000 and not more than 20,000 inhabitants, and  

   Fourth class -- Those having not more than 10,000 inhabitants.