SDCL § 9-2-1: Classes enumerated--Population groups.

The three classes of municipal corporations are:

(1) Municipalities of the first class: municipal corporations with a population of five thousand and over;

(2) Municipalities of the second class: municipal corporations with a population between five hundred and four thousand nine hundred ninety-nine;

(3) Municipalities of the third class: municipal corporations with a population of fewer than five hundred.