Missouri Municipalities
Missouri statutes classify municipalities on the basis of population and limit the form of government options of each classification. The statutes provide that a community may incorporate as a city of the third class, fourth class or village on the basis of the population at the time of incorporation. 1Once a community is incorporated under a given classification, the municipality does not automatically change classification with a gain or loss of population. A municipality may change classification only when the change is approved by a majority vote of the people. There are certain forms of government permitted for each classification of municipality. Villages are permitted only one form of government—an elected board of trustees, five in number if the village has less than 2,500 population and nine if more than 2,500 population. Fourth-class cities are permitted to have either the mayor/board of aldermen form or the mayor/city administrator/aldermen form. The board of aldermen may adopt the city administrator form by ordinance, without a vote of the people. Third-class cities are granted greater flexibility with the authority to establish the mayor/council form, the council/manager form, the commission form or the mayor/city administrator/council form. Finally, constitutional charter cities may adopt any form of government that the people approve in the charter.
Source: https://www.sos.mo.gov/CMSImages/Publications/municipalities05.pdf