How to Adopt an Adult in Montana

Reviewed by DocDraft Legal Team · Montana · Last updated November 13, 2026

Once you have adopted one grown person in Montana, the law makes you wait a year before adopting another, unless the second person is the first one's brother or sister. Adult adoption is a district court proceeding in which one adult becomes the permanent legal parent of another adult, with the inheritance and family consequences that follow. Montana sets the rules in five short sections, MCA 42-4-401 through 42-4-405. Any person 18 or older may be adopted by another adult, with no category list and no minimum age gap, but you may not adopt your own spouse. Consent is required only of three people: the person being adopted, you as the adopting parent, and your husband or wife. Part 4 asks your spouse for a signed consent, and the court may go ahead without it if you are legally separated or if the judge finds your spouse incapable of consenting or withholding consent against the best interests of you both. The adoptee's parents do not consent, and the adoptee's own spouse is not on the list. You must have lived in Montana for at least 90 days before filing, and you file in the district court of the county where you live. The clerk's fee schedule lists $75 for an adoption petition. Montana switches off the preplacement evaluation and postplacement supervision for adults, but an adult who is legally incompetent is adopted under all the rules for a child. Attorney review of your documents is available through DocDraft.

Find out where you stand in Montana

Who are you hoping to adopt?

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Who can be adopted as an adult in Montana?

Any person who has reached 18, the age of legal majority, may be adopted by another adult (MCA 42-4-401, 42-4-402). There is no category list and no required age gap. You may not adopt your own spouse, and an incompetent adult must be adopted under all the requirements that govern adopting a child.

Whose consent is needed for an adult adoption in Montana?

Only three people: the person being adopted, the adopting parent, and the adopting parent's spouse (MCA 42-4-403(1)). The adoptee's parents are not asked (MCA 42-4-401). The spouse's consent is excused if the couple is legally separated or the court finds the spouse incapable or unreasonably withholding consent.

How long must I live in Montana before filing an adult adoption?

At least 90 days immediately before the petition is filed. The district court has jurisdiction over an adult adoption only if the petitioner meets that period (MCA 42-4-404(1)). The petition then goes to the district court in the county where a petitioner lives (MCA 42-4-404(2)).

Can I adopt more than one adult in Montana?

Yes, but not within one year of the first adoption unless the second person is a sibling of the first adoptee (MCA 42-4-402(2)). The bar applies to anyone who has adopted an adult or an emancipated minor, so adopting two unrelated adults means filing at least a year apart.

Montana adult adoption at a glance

In Montana an adult adoption is a district court decree that makes one adult the legal parent of another, with all the rights and duties of a parent and child (MCA 42-5-202). Eligibility is open to anyone 18 or older, apart from your own spouse. Two rules deserve early attention. First, the adopting parent signs a consent alongside the adoptee, and both consents must say you understand what the adoption may do to inheritance, property and support. Second, after one adult adoption you must wait a year before another unless the new adoptee is a sibling of the first. Your husband or wife must also consent unless you are legally separated or the court excuses it. The petitioner needs 90 days of Montana residency. The Judicial Branch publishes a free adult adoption packet.

Two foster brothers, one Cascade County household and the one year rule

A retired rancher in Great Falls took in two brothers, Eli and Sam, when they were 13 and 15, and both are now in their twenties. He adopts Eli first, using the court's packet, and his second wife signs the spouse consent on form AA 400 because she is not legally separated from him. Five months later Sam asks to be adopted too. Ordinarily MCA 42-4-402(2) would make the rancher wait a full year after Eli's decree, but Sam is Eli's brother, so the sibling exception lets the second petition go in now. He has lived in Montana for decades, so the 90 day rule is met, and he files again in Cascade County. Because both brothers lived in his home as minors, gifts by his relatives to his children can reach them under MCA 72-2-715(3).

Relevant Laws

MCA 42-4-401 and 42-4-402 (who may adopt and be adopted)

Any person who has reached the age of legal majority may be adopted without the consent of the person's parents. An adult may adopt another adult but not the adult's spouse, an incompetent person of any age is adopted under the rules for a child, and a second adult adoption must wait a year unless the adoptees are siblings.

MCA 42-4-403 (the three consents)

Limits consent to the adoptee, the prospective adoptive parent and that parent's spouse, sets when the spouse's consent is excused, and requires each consent in writing, signed before the court or a person authorized to take acknowledgments, with a statement about inheritance, property and support.

MCA 42-4-404 and 42-4-405 (residency, venue and procedure)

The district court has jurisdiction if the petitioner has lived in Montana at least 90 days before filing, and the petition is filed in a petitioner's county. The child adoption procedure applies to adults except as Part 4 provides, with the preplacement and postplacement evaluation rules switched off.

MCA 25-1-201(1)(q) (adoption petition fee)

The clerk of district court fee schedule lists $75 for filing a petition for adoption. The same section sets other clerk charges, including a general fee at the commencement of an action or proceeding, so confirm the total due with the clerk.

MCA 72-2-124 and 72-2-715 (inheritance)

Section 72-2-124(2) makes an adopted person the child of the adopting parent and not of the natural parents for intestate succession, with an exception for adoption by a natural parent's spouse. Section 72-2-715(3) limits gifts to a class such as children to an adoptee who lived in the adopting parent's household as a minor.

Regional Variances

Montana adult adoption rules at a glance

Who may be adopted

Any person who has reached 18, the age of legal majority (MCA 42-4-401, 41-1-101). No category list. You may not adopt your own spouse (MCA 42-4-402(1)). Part 4 also covers emancipated minors.

Incompetent adoptee

An adoption of an incompetent individual of any age must comply with all requirements set by law for the adoption of a child (MCA 42-4-402(1)). The adult consent list and the adult evaluation waiver do not settle that case.

One year limit

After adopting an adult or emancipated minor, you may not adopt another within one year unless the new adoptee is a sibling of the first (MCA 42-4-402(2)).

Age relationship

None. Title 42 sets no minimum number of years between you and no requirement that the adoptee be younger.

Consent of the adoptee and the adopting parent

Both required, in writing, signed before the court or a person authorized to take acknowledgments, stating that you agree to the parent and child relationship and understand its effect on inheritance, property and support (MCA 42-4-403(2)).

Consent of the adopting parent's spouse

Required unless legally separated, or the court finds the spouse incapable of consenting or withholding consent contrary to the best interests of the adoptee and adopting parent (MCA 42-4-403(1)(c)). Part 4 asks for consent, not joinder; the packet uses a separate spouse consent, form AA 400.

Consent of the adoptee's spouse

Not required. MCA 42-4-403(1) limits consent to the adoptee, the adopting parent and the adopting parent's spouse.

Birth parents

No consent (MCA 42-4-401). No Part 4 provision requires notice to them, though the court may name any person to receive notice (MCA 42-5-103(1)(f)).

Court and venue

District court of the county in which a petitioner lives (MCA 42-1-103(8), 42-4-404(2)).

Residency

The petitioner must have lived in Montana at least 90 days immediately before filing (MCA 42-4-404(1)). Part 4 sets no residency rule for the adoptee.

Filing fee

$75 for filing a petition for adoption under MCA 25-1-201(1)(q). Confirm the full amount due with the clerk of district court.

Home study and evaluations

Expressly switched off for adults: adoptive decision support services, preplacement evaluation, postplacement supervision period and postplacement evaluation (MCA 42-4-405), except for an incompetent adoptee.

Hearing and notice

The court holds a hearing on the petition and may waive the adoptee's presence (MCA 42-5-105). A spouse who has not joined the petition gets notice unless the spouse consented in writing or waived notice (MCA 42-5-103).

Name and birth certificate

The statutes allow a new name in the petition and decree (MCA 42-5-101(1)(e), 42-5-109(5)), but the packet is printed to keep the name unchanged. An adoptee 12 or older may ask that no new birth certificate issue (MCA 42-5-109(6)).

Inheritance

Intestacy follows Title 72 (MCA 42-5-202(3)): child of the adopting parent, not the natural parents, with a natural parent's spouse exception (MCA 72-2-124(2)). Class gifts by others reach the adoptee only if raised in your household as a minor (MCA 72-2-715(3)).

Forms

Montana Judicial Branch Adult Adoption Forms packet, AA 100 through AA 600, last revised June 20, 2024. The petition and consents must be notarized.