SDCL § 9-2-2: Population determined by census--Estimate by election totals after change of municipal boundaries.

For the purpose of classification, the population of each municipality is determined by the last preceding federal census. Whenever the municipal boundaries included in the last preceding census substantially differ from the current boundaries of the municipality, the governing body by resolution may direct the finance officer to determine the population by filing a certificate showing the number of persons who voted at the last preceding annual municipal election. That number multiplied by three constitutes the population for the purpose of classification until the next federal census is completed.