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South Dakota Codified Laws

S.D. Codified Laws § 53-4-9 (2026)

Mistake of fact defined.

✓ current as of May 2026
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53-4-9. Mistake of fact defined.

Mistake of fact is a mistake not caused by the neglect of a legal duty on the part of the person making the mistake and consisting in:

(1)    An unconscious ignorance or forgetfulness of a fact, past or present, material to the contract; or

(2)    Belief in the present existence of a thing material to the contract which does not exist, or in the past existence of such a thing which has not existed.

Source: CivC 1877, § 888; CL 1887, § 3512; RCivC 1903, § 1206; RC 1919, § 821; SDC 1939, § 10.0312.

Notes of Decisions
Cited in 16 cases, 1981–2018 · leading case: McDonald v. Miners & Merchants Bank, Inc., 310 N.W.2d 591 (S.D. 1981).
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McDonald v. Miners & Merchants Bank, Inc., 310 N.W.2d 591 (S.D. 1981). · cites it 7× “Mistake is defined in SDCL 53-4-9: *593 Mistake of fact is a mistake not caused by the neglect of a legal duty on the part of the person making the mistake and consisting in: (1) An unconscious ignorance or forgetfulness of a fact, past or present, material to the contract; or…”
LPN Trust v. Farrar Outdoor Advert., Inc., 1996 SD 97 (S.D. 1996). · cites it 4× “SDCL 53-4-9 defines mistake of fact as "a mistake not caused by the neglect of a legal duty on the part of the person making the mistake.”
In Re Est. of Smid, 2008 SD 82 (S.D. 2008). · cites it 4× “SDCL 53-4-9. Audrey alleges that her lack of knowledge of Ronald's financial holdings constitutes a mistake of fact.”
Nemec v. Deering, 350 N.W.2d 53 (S.D. 1984). · cites it 4× “NOTES [*] SDCL 53-4-9 provides: Mistake of fact is a mistake not caused by the neglect of a legal duty on the part of the person making the mistake and consisting in: (1) An unconscious ignorance or forgetfulness of a fact, past or present, material to the contract;.”
Knudsen v. Jensen, 521 N.W.2d 415 (S.D. 1994). · cites it 2× “SDCL 53-4-9 defines mistake of fact as, *418 [A] mistake not caused by the neglect of a legal duty on the part of the person making the mistake and consisting in: (1) An unconscious ignorance or forgetfulness of a fact past or present, material to the contract; or (2) Belief in…”
Harding Cnty., Sd v. Frithiof, 575 F.3d 767 (8th Cir. 2009). · cites it 2× “See SDCL §§ 53-4-9, 53-11-2. Rescission for mistake of fact requires that the mistake "not result from the want of such care and diligence as would be exercised by a person of reasonable prudence under the same circumstances.”
Maasjo v. McLaughlin Sch. Dist. 15-2, 489 N.W.2d 618 (S.D. 1992). · cites it 2× “*623 Additionally, under SDCL 53-4-9: Mistake of fact is a mistake not caused by the neglect of a legal duty on the part of the person making the mistake and consisting in: (1) An unconscious ignorance or forgetfulness of a fact, past or present, material to the contract; or (2)…”
Home Bldg. & Loan Ass'n v. Perpetual Sav. & Loan Ass'n of Rapid City, South Dakota, 338 N.W.2d 456 (S.D. 1983). · cites it 3× “3 A mistake may be either one of fact, SDCL 53-4-9, or one of law, SDCL 53 — 1—10.”
First Colony Life Ins. Co. v. Daniel R. Berube v. Nancy R. Cox, Also Known as Nancy R. Walker, 130 F.3d 827 (1st Cir. 1997). “See S.D. Codified Laws § 53-4-9 ; Sutherland v.”
Carnicle v. Swann, 314 N.W.2d 311 (S.D. 1982). · cites it 5× “SDCL 53-4-9 defines mistake: Mistake of fact is a mistake not caused by the neglect of a legal duty on the part of the person making the mistake and consisting in: (1) An unconscious ignorance or forgetfulness of a fact, past or present, material to the contract; or (2) Belief…”
Vermilyea v. BDL Enter., Inc., 462 N.W.2d 885 (S.D. 1990). “[i]f [the] consent of the party rescinding ... was given by mistake or obtained through .”
Wolken v. Wade, 406 N.W.2d 720 (S.D. 1987). “Furthermore, since the character of title depended on Wades’ ability to cure within a reasonable time after performance was due, it is evident that any mistake was not based on a present or existing fact but a future fact.”
Show all 16 citing cases →
— S.D. Codified Laws § 53-4-9(1) — 2 cases
Nemec v. Deering, 350 N.W.2d 53 (S.D. 1984). “NOTES [*] SDCL 53-4-9 provides: Mistake of fact is a mistake not caused by the neglect of a legal duty on the part of the person making the mistake and consisting in: (1) An unconscious ignorance or forgetfulness of a fact, past or present, material to the contract;.”
Schaefer v. Sioux Spine & Sport, Prof. LLC, 2018 SD 5 (S.D. 2018).
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