S.D. Codified Laws § 10-21-23
On May first of the year after which taxes have been assessed, one-half of all unpaid real property taxes are delinquent. However, all real property taxes totaling fifty dollars or less shall be paid in full on or before April thirtieth. On May first and the first day of each month thereafter there shall be added as interest on the delinquent taxes at the Category G rate of interest as established in § 54-3-16. If the other half is not paid on or before October thirty-first of the same year, that amount also becomes delinquent on November first and the same interest shall attach in the same manner. If the last day of April or October falls on a Saturday or Sunday, the tax is due and payable on the last working day of that month. The tax payment shall either be received in the office on the last working day or the tax payment shall be postmarked by the last day before the taxes become delinquent.
SDCL 10-21-23