S.D. Codified Laws § 10-25-7
The notice to the holder of any special assessment certificate shall be directed to the certificate holder at the address that appears for the certificate holder in connection with the record of the certificate with the finance officer of the municipality. The notice shall be personally served or sent by registered or certified mail, return receipt requested. A like notice, by personal service or registered or certified mail, return receipt requested, shall be sent to the holder of any tax certificate issued upon a sale for any special assessment, by mailing to the tax certificate holder's address as the address appears in the office of the treasurer. Service is not required for any tax certificate holder whose name and address do not appear in the record and for whom an affidavit or tax certificate is made by the treasurer stating that the person's name or address is not known to the treasurer, accompanied by an affidavit of the holder of the tax certificate that the holder does not know the name and address of the person.
SDCL 10-25-7