SDCL § 21-41-6: Joinder of unknown claimants as defendants--Proof of want of knowledge.

If not known, the persons named in § 21-41-5 may be made defendants by designating them in the summons and complaint as, all persons unknown who have or claim to have any interest or estate in or lien or encumbrance upon the premises described in the complaint. In case unknown parties are so made defendants, the complaint shall state and the proof show that if there are any persons whomsoever who have any interest or estate in, claim to, or lien or encumbrance upon the premises other than the defendants named, they were unknown at the time of the commencement of the action.