Mont. Code Ann. » TITLE 40. FAMILY LAW · CHAPTER 1. MARRIAGE · Part 4. Validity of Marriages -- Declaration of Invalidity
Montana Code Annotated

Mont. Code Ann. § 40-1-402 (2026)

Declaration Of Invalidity

✓ current as of May 2026
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  1. MCA Contents
  2. TITLE 40
  3. CHAPTER 1
  4. Part 4
  5. 40-1-402 Declaration of invalidity

TITLE 40. FAMILY LAW

CHAPTER 1. MARRIAGE

Part 4. Validity of Marriages -- Declaration of Invalidity

Declaration Of Invalidity

40-1-402. Declaration of invalidity. (1) The district court shall enter its decree declaring the invalidity of a marriage entered into under the following circumstances:

(a) a party lacked capacity to consent to the marriage at the time that the marriage was entered into, either because of mental incapacity or infirmity or because of the influence of alcohol, drugs, or other incapacitating substances, or a party was induced to enter into a marriage by force or duress or by fraud involving the essentials of marriage;

(b) a party lacks the physical capacity to consummate the marriage by sexual intercourse, and at the time that the marriage was entered into, the other party did not know of the incapacity;

(c) a party was under 16 years of age or was 16 or 17 years of age and did not have the consent of the party's parents or guardian or judicial approval; or

(d) the marriage is prohibited.

(2) A declaration of invalidity under subsections (1)(a) through (1)(c) may be sought by any of the following persons and must be commenced within the times specified, but a declaration of invalidity may not be sought after the death of either party to the marriage:

(a) for lack of capacity to consent because of mental incapacity or infirmity, no later than 1 year after the petitioner obtained knowledge of the described condition;

(b) for lack of capacity to consent because of the influence of alcohol, drugs, or other incapacitating substances, no later than 1 year after the petitioner obtained knowledge of the described condition;

(c) for lack of capacity to consent because of force, duress, or fraud, no later than 2 years after the petitioner obtained knowledge of the described condition;

(d) for the reason set forth in subsection (1)(b), by either party, no later than 4 years after the petitioner obtained knowledge of the described condition;

(e) for the reason set forth in subsection (1)(c), by the underaged party or the party's parent or guardian, before the time that the underaged party reaches the age at which the party could have married without satisfying the omitted requirement.

(3) A declaration of invalidity for the reason set forth in subsection (1)(d) may be sought by either party, the legal spouse in case of a bigamous marriage, the county attorney, or a child of either party, at any time before the death of one of the parties.

(4) Children born of a marriage declared invalid are legitimate.

(5) Unless the court finds, after a consideration of all relevant circumstances, including the effect of a retroactive decree on third parties, that the interests of justice would be served by making the decree not retroactive, it shall declare the marriage invalid as of the date of the marriage. The provisions of chapter 4 relating to property rights of the spouses, maintenance, support, and parenting of children on dissolution of marriage are applicable to nonretroactive decrees of invalidity.

(6) The clerk of the court shall give notice of the entry of a decree declaring the invalidity of a marriage:

(a) if the marriage is registered in this state, to the clerk of the district court of the county where the marriage is registered, who shall enter the fact of invalidity in the book in which the marriage license and certificate are recorded; or

(b) if the marriage is registered in another jurisdiction, to the appropriate official of that jurisdiction, with the request that the official enter the fact of invalidity in the appropriate record.

History: En. 48-311 by Sec. 11, Ch. 536, L. 1975; amd. Sec. 1, Ch. 279, L. 1977; R.C.M. 1947, 48-311; amd. Sec. 1, Ch. 109, L. 1995; amd. Sec. 4, Ch. 343, L. 1997.

Notes of Decisions
Cited in 8 cases (1 in the last 5 years), 1979–2025 · leading case: In Re Marriage of Adams, 604 P.2d 332 (Mont. 1979).
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In Re Marriage of Adams, 604 P.2d 332 (Mont. 1979). · cites it 36× “The public policy in Montana against marriages between first cousins is buttressed by the provisions of section 40-1-402, MCA, which states when the District Court shall enter its decree declaring the invalidity of a marriage prohibited by law.”
In Re the Marriage of Williams, 677 P.2d 585 (Mont. 1984). · cites it 9× “In the statutory scheme provided by Section 40-1-402, MCA, in allowing annulments to be made nonretroactive, there is no provision as to which court, the court having jurisdiction of the annulment cause, or the court having jurisdiction of the dissolution cause, should determine…”
In Re the Marriage of Helsel, 723 P.2d 963 (Mont. 1986). · cites it 12× “Did the District Court err when it declared the marriage of the parties invalid under Section 40-1-402, MCA, on the basis of immaturity of the parties? 2.”
In Re the Marriage of Wolf, 2011 MT 192 (Mont. 2011). · cites it 20× “¶ 23 However, § 40-1-402(5), MCA, provides that a declaration of marriage invalidity may be retroactive to the date of the marriage.”
Est. of Cook, 2020 MT 240 (Mont. 2020). · cites it 5× “¶38 Section 40-1-402(1)(a), MCA, provides that: The district court shall enter its decree declaring the invalidity of a marriage entered into under the following circumstances: (a) A party lacked capacity to consent to the marriage at the time that the marriage was entered into,…”
In re the Est. of Schanbacher, 595 P.2d 1171 (Mont. 1979). · cites it 3× “1947, now section 40-1-402(2) MCA, provides: “(2) Parties to a marriage prohibited under this section who cohabit after removal of the impediment are lawfully married as of the date of the removal of the impediment.”
In Re the Est. of Flynn, 908 P.2d 661 (Mont. 1995). · cites it 5× “ISSUE 1 Did the District Court err in invalidating the marriage of Joseph and Mary Flynn? Section 40-1-402, MCA, sets forth the grounds upon which a district court may declare a marriage invalid.”
Marriage of Anderson, 2025 MT 213 (Mont. 2025). · cites it 9× “¶12 Here, neither the District Court’s findings of fact nor its conclusions of law demonstrate a determination of the marriage being invalid under § 40-1-402, MCA. Rather, the District Court only determined that the marriage was irretrievably broken.”
Mont. Code Ann. § 40-1-402(1): 1 case
Marriage of Anderson, 2025 MT 213 (Mont. 2025). “¶12 Here, neither the District Court’s findings of fact nor its conclusions of law demonstrate a determination of the marriage being invalid under § 40-1-402, MCA. Rather, the District Court only determined that the marriage was irretrievably broken.”
Mont. Code Ann. § 40-1-402(1)(a): 2 cases
In Re the Marriage of Helsel, 723 P.2d 963 (Mont. 1986). “Did the District Court err when it declared the marriage of the parties invalid under Section 40-1-402, MCA, on the basis of immaturity of the parties? 2.”
Est. of Cook, 2020 MT 240 (Mont. 2020). “¶38 Section 40-1-402(1)(a), MCA, provides that: The district court shall enter its decree declaring the invalidity of a marriage entered into under the following circumstances: (a) A party lacked capacity to consent to the marriage at the time that the marriage was entered into,…”
Mont. Code Ann. § 40-1-402(2): 2 cases
Est. of Cook, 2020 MT 240 (Mont. 2020). “¶38 Section 40-1-402(1)(a), MCA, provides that: The district court shall enter its decree declaring the invalidity of a marriage entered into under the following circumstances: (a) A party lacked capacity to consent to the marriage at the time that the marriage was entered into,…”
In re the Est. of Schanbacher, 595 P.2d 1171 (Mont. 1979). “1947, now section 40-1-402(2) MCA, provides: “(2) Parties to a marriage prohibited under this section who cohabit after removal of the impediment are lawfully married as of the date of the removal of the impediment.”
Mont. Code Ann. § 40-1-402(5): 3 cases
In Re Marriage of Adams, 604 P.2d 332 (Mont. 1979). “The public policy in Montana against marriages between first cousins is buttressed by the provisions of section 40-1-402, MCA, which states when the District Court shall enter its decree declaring the invalidity of a marriage prohibited by law.”
In Re the Marriage of Williams, 677 P.2d 585 (Mont. 1984). “In the statutory scheme provided by Section 40-1-402, MCA, in allowing annulments to be made nonretroactive, there is no provision as to which court, the court having jurisdiction of the annulment cause, or the court having jurisdiction of the dissolution cause, should determine…”
In Re the Marriage of Wolf, 2011 MT 192 (Mont. 2011). “¶ 23 However, § 40-1-402(5), MCA, provides that a declaration of marriage invalidity may be retroactive to the date of the marriage.”
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