S.D. Codified Laws § 15-6-33(a)
Any party may serve upon any other party written interrogatories to be answered by the party served or, if the party served is a public or private corporation or a partnership or association or governmental agency, by any officer or agent, who shall furnish such information as is available to the party. Interrogatories may, without leave of court, be served upon the plaintiff after commencement of the action and upon any other party with or after service of the summons and complaint upon that party.
Each interrogatory shall be answered separately and fully in writing under oath, unless it is objected to, in which event the objecting party shall state the reasons for the objection and shall answer to the extent the interrogatory is not objectionable. The answers are to be signed by the person making them, and the objections signed by the attorney making them. The party upon whom the interrogatories have been served shall serve a copy of the answers, and objections, if any, within thirty days after the service of the interrogatories, except that a defendant may serve answers or objections within forty-five days after service of the summons and complaint upon that defendant. A shorter or longer time may be directed by the court or, in the absence of such order, agreed to in writing by the parties. All grounds for an objection to an interrogatory shall be stated with specificity. Any ground not stated in a timely objection is waived unless the party's failure to object is excused by the court for good cause shown. The party submitting the interrogatories may move for an order under § 15-6-37(a) with respect to any objection to or other failure to answer an interrogatory. A party answering interrogatories must set out the interrogatory immediately preceding the answer thereto.
SDCL 15-6-33(a)