A Montana common law marriage exists when two people who are legally free to marry agree to be married and then live together while holding themselves out to the community as spouses. No license, ceremony, or officiant is required. Once those elements are met, the relationship is a marriage in every legal sense: the couple has the same property rights, inheritance rights, tax status, and divorce obligations as any couple who stood before a judge or minister.
Montana is one of a small number of states that still allows this. The governing statute, MCA 40-1-403, is a single sentence saying common law marriages “are not invalidated” by the rest of Montana’s marriage code, leaving the real rules to the courts.1Montana State Legislature. Montana Code 40-1-403 – Validity of Common-Law Marriage
The Three Elements Montana Courts Require
The Montana Supreme Court, in Matter of Estate of Hunsaker and later Matter of Estate of Ober, settled on a three-part test. Whoever claims the marriage exists has to prove all three.2Montana Supreme Court. In the Matter of the Estate of John Louis Ober (2003 MT 7)
Competency. Both partners must be at least 18, mentally capable of understanding what they are agreeing to, not already married to someone else, and not closely related. Neither can be under the influence of drugs or alcohol when the agreement is formed.3Montana Judicial Branch. Marriage – Common Law Marriage – Getting Married
Mutual agreement. Both must form a present intent to be married, right now, and express that intent to each other. The agreement does not have to follow any particular form, and it can be inferred from conduct, but it has to be real. Nobody drifts into a common law marriage in Montana just by living with a partner.4Montana State University. Montana Common Law Marriages and Estate Planning
Cohabitation and public repute. The couple must live together and present themselves to the world as married: shared last name, introductions as husband or wife, behaving as spouses in daily life. Because this takes time to develop, the court does not require all three elements to click into place on the same day.4Montana State University. Montana Common Law Marriages and Estate Planning
How You Prove a Common Law Marriage
Courts weigh the whole picture rather than any single document. Useful evidence includes joint tax returns, joint bank accounts, a shared mortgage, insurance beneficiary designations naming each other as spouse, and testimony from friends and family who understood the couple to be married.3Montana Judicial Branch. Marriage – Common Law Marriage – Getting Married
No single factor decides it. The Montana Judicial Branch has said that keeping separate finances does not automatically defeat a claim, and sharing accounts does not automatically create one. The court looks at how the couple actually lived against the backdrop of Montana’s public policies on marriage.3Montana Judicial Branch. Marriage – Common Law Marriage – Getting Married
The practical problem is timing. These disputes almost always come up after a death or breakup, when the other party (or their heirs) has a strong financial reason to deny the marriage ever existed. Without a license on file anywhere, the surviving or claiming partner is left reconstructing years of life from paperwork and witnesses. Couples who believe they are common law married are far better off gathering that proof while the relationship is intact.
A Simpler Option: The Declaration of Marriage
Montana offers a middle path. Under MCA 40-1-311, two people can file a signed, witnessed written declaration of marriage with the clerk of the district court in the county where they live. No ceremony, no officiant. The declaration lists both parties’ names, ages, and addresses, their parents’ names, a statement of legal competency, and the signatures of the couple and at least two witnesses, acknowledged before the clerk. The filing fee is $53.5FindLaw. Montana Title 40 Family Law 40-1-311
The declaration produces something a pure common law marriage does not: a government-filed record. For couples who want the informality of common law marriage without the evidentiary mess that often follows, filing a declaration solves the proof problem before it starts. MCA 40-1-403 preserves the validity of declarations alongside common law marriages.1Montana State Legislature. Montana Code 40-1-403 – Validity of Common-Law Marriage
What a Common Law Marriage Means for Your Rights
Once established, a common law marriage carries identical legal weight to a ceremonial one. The consequences reach into property, support, inheritance, children, and taxes.
Property
If the marriage ends, Montana treats all property belonging to either or both spouses as subject to equitable division, regardless of whose name is on the title and regardless of when it was acquired. The court weighs the length of the marriage, each spouse’s age, health, income, and employability, each person’s contribution to the household (homemaking counts), and whether either spouse wasted marital assets. “Equitable” does not have to mean 50/50; the judge has broad discretion. Property brought into the marriage or received by gift or inheritance is still considered, though the court weighs the other spouse’s contribution to maintaining or growing it.6Montana State Legislature. Montana Code 40-4-202 – Division of Property
Maintenance
A common law spouse can request maintenance (Montana’s word for alimony) if they lack sufficient property to meet reasonable needs and cannot support themselves through work, or if they are caring for a child whose circumstances make outside employment impractical. The court sets amount and duration based on the requesting spouse’s resources, time needed for education or training, the standard of living during the marriage, the length of the marriage, and the paying spouse’s ability to meet the obligation while covering their own needs.7Montana State Legislature. Montana Code 40-4-203 – Maintenance
Inheritance
A surviving common law spouse has the same inheritance rights as any other spouse. If the deceased partner left no will, the surviving spouse takes a share set by Montana’s intestacy statute, with the exact amount depending on whether there are surviving parents, shared children, or children from other relationships.8Montana State Legislature. Montana Code 72-2-112 – Share of Spouse
The flip side is severe. If the surviving partner cannot prove the marriage existed, they inherit nothing under intestacy, and the entire estate goes to the deceased’s blood relatives. That is exactly the fight that produced Hunsaker and Ober, and it is the single strongest reason to document the marriage early.4Montana State University. Montana Common Law Marriages and Estate Planning
Children
Children born during a common law marriage are legitimate children of that marriage under MCA 40-6-201. If the couple separates, a parenting plan is required just as in any other divorce.3Montana Judicial Branch. Marriage – Common Law Marriage – Getting Married
Ending a Common Law Marriage
There is no informal way out. Dissolving a common law marriage requires the same divorce petition in district court as any other marriage. The filing spouse must have been domiciled in Montana (or stationed there in the armed services) for at least 90 days, and the marriage must be irretrievably broken, which Montana presumes if the spouses have lived apart for more than 180 days or if there is serious marital discord affecting either partner.9Montana State Legislature. Montana Code 40-4-104 – Dissolution of Marriage – Legal Separation
One extra step applies. Before dividing property or awarding maintenance, the court first has to confirm the common law marriage actually existed. The spouse claiming the marriage must prove the same three elements that created it. Only then does the case proceed as a standard dissolution covering property, maintenance, and parenting.9Montana State Legislature. Montana Code 40-4-104 – Dissolution of Marriage – Legal Separation
Federal Recognition and Moving Out of State
The IRS treats you as married for federal tax purposes if you have a valid common law marriage under state law, and this stays true even if you later move to a state that does not recognize common law marriage. You must file as married filing jointly or married filing separately; you cannot file as single.10Internal Revenue Service. Revenue Ruling 2013-17
Social Security does the same for survivor and dependent benefits. To establish the marriage after a spouse’s death, SSA asks for your own signed statement affirming the marriage plus signed statements from two blood relatives of the deceased (or other people if blood relatives are unavailable) explaining why they believe the marriage was valid.11Social Security Administration. Code of Federal Regulations 404.726 – Evidence of Common-Law Marriage
A Montana marriage generally remains valid if you move. The Full Faith and Credit Clause requires other states to honor judicial proceedings and public acts from Montana.12Office of the Law Revision Counsel. 28 U.S. Code 1738 – State and Territorial Statutes and Judicial Proceedings The complication is when no court has ever formally recognized the marriage. If you move to a state that does not permit common law marriages and later need to prove yours existed, you may face skeptical judges and limited procedures. Filing a declaration or securing a court recognition while still in Montana avoids that problem.
Who Cannot Form a Common Law Marriage
The capacity rules track those for a licensed marriage. Both partners must be at least 18, both must have mental capacity, and neither can be intoxicated when the agreement is formed.3Montana Judicial Branch. Marriage – Common Law Marriage – Getting Married
Montana prohibits marriages between ancestors and descendants, siblings (including half-siblings), and uncles or aunts with nieces or nephews. A marriage attempted while either party is still legally married to someone else is also void, and entering into one is bigamy, punishable by a fine of up to $500, up to six months in jail, or both.13Montana State Legislature. Montana Code 45-5-611 – Bigamy
If you are separated from a prior spouse but do not yet have a final divorce decree, you cannot form a valid common law marriage with a new partner. Years of living apart do not substitute for a court order ending the earlier marriage.