Detailed answer

Short answer: Yes. If a co‑owner died, the deceased co‑owner’s ownership interest passes to that person’s estate or heirs, and those successors must be included (joined) in a Missouri partition action if their legal interest affects the property. How you add them depends on whether a personal representative (executor/administrator) has been appointed in probate, whether the heirs are known, and whether any heirs are minors or unknown. Missouri’s partition statutes and general civil procedure permit joining heirs, substituting a personal representative, using service by publication for unknown heirs, and appointment of a guardian ad litem when necessary.

Why heirs or an estate must be included

Partition divides legal interests in real property between co‑owners. When a co‑owner dies, that co‑owner no longer appears on the title personally; their ownership interest vests in a personal representative (if the decedent’s estate is opened) or in the heirs/devisees by operation of Missouri succession law. Because the successor(s) hold the legal interest that you seek to partition, they are necessary or indispensable parties to a partition action.

Key Missouri law (where to look)

Missouri statutes on partition of real estate (Chapter 525) – general rules on who may maintain partition and how the court divides or sells property: RSMo Chapter 525 – Partition of Real Estate.
Missouri statutes on intestate succession and distribution to heirs (Chapter 474) — helpful to determine who are the heirs if no will and probate has not been opened: RSMo Chapter 474 – Descent and Distribution.
Missouri probate and personal representative rules — if the estate is open you will usually join the personal representative as the party who represents the decedent’s interest.

Typical scenarios and what to do

Scenario A — Probate already opened and a personal representative (PR) appointed

Action: Name and serve the personal representative as a party on behalf of the estate. The PR is the proper party to represent the decedent’s interest in litigation and may be joined in the partition petition or substituted for the decedent.

Scenario B — No probate opened, heirs are known

Action: Identify and join the heirs (or devisees named in a will) as defendants in the partition petition. If the heirs accept service, they become parties and the court can proceed to partition their interests. If an heir is a minor or incapable, the court will require a guardian or guardian ad litem to protect that interest.

Scenario C — Heirs unknown or cannot be located

Action: Missouri courts permit alternative service (publication) and joinder of “unknown heirs” or “heirs at law unknown.” You must follow the court’s local rules and statutory requirements for service by publication and show reasonable diligence to locate heirs. The court may appoint a guardian ad litem or a curator to represent unknown or unascertained interests before distributing proceeds.

Scenario D — Multiple heirs with conflicting claims

Action: Join all claimants, allow the court to determine ownership percentages, and proceed with partition in kind or by sale. If the court orders sale, proceeds are divided according to the interest each party holds after judicial determination.

Step‑by‑step practical procedure to add heirs to a partition action in Missouri

Confirm who owned the interest at death — check the deed, title, and whether the co‑owner owned the property as joint tenants with right of survivorship, tenants in common, or some other form. Survivorship language changes the result: joint tenancy may pass automatically to surviving joint tenant(s) and you may not need heirs.
Search for a probate file — if a probate case exists, obtain the name and contact information for the personal representative from the probate court records. If a PR exists, name and serve the PR in the partition case.
Identify heirs — use a title company, genealogical search, or probate records to locate heirs (spouse, children, parents, siblings, etc., per RSMo intestacy rules).
Name parties in the petition — list each heir or devisee you can find. If some heirs are unknown, include a party described as “heirs and devisees of [Name], unknown” so the court knows there may be additional claimants.
Serve process correctly — personally serve known heirs or the PR. For unknown/unlocatable heirs, follow Missouri rules for service by publication and file affidavits showing efforts to locate them.
If a party is a minor or incapacitated — request appointment of a guardian ad litem or ask the court to appoint counsel to protect that party’s interest before final distribution.
Ask the court for appropriate relief — partition in kind (divide the property), partition by sale, appointment of a commissioner to sell, or appointment of a receiver, and ask the court to determine each party’s share.

Evidence and documents you will need

Current deed and chain of title showing the deceased co‑owner’s interest.
Death certificate for the deceased co‑owner.
Probate case number and letters testamentary/letters of administration if a PR has been appointed.
Affidavits or documents proving efforts to locate missing heirs (if using publication).
Birth, marriage, and other family documents to establish heirship if intestate succession will control.

Common complications and how courts handle them

If the decedent owned the property as a joint tenant with survivorship, heirs typically do not inherit the decedent’s interest — the surviving joint tenant(s) own the property outright. Confirm the manner of holding title.
When heirs cannot be located, courts may allow service by publication and appoint a representative to protect unknown interests before sale or distribution.
Partition can be paused if probate administration is necessary to determine the ownership interest or if estate debts must be addressed first.

When to consider alternative steps instead of immediate partition

Open probate first if estate assets or debts must be settled and title needs clarifying.
Negotiate a buy‑out with heirs or co‑owners to avoid costly litigation.
Mediation can resolve disputes about shares, costs, or management before asking the court to sell or divide the property.

Helpful links and resources

Missouri Revised Statutes — Chapter 525 (Partition of Real Estate): https://revisor.mo.gov/main/Chapters.aspx?chapter=525
Missouri Revised Statutes — Chapter 474 (Descent and Distribution / Intestate Succession): https://revisor.mo.gov/main/Chapters.aspx?chapter=474
Local county probate court website — to check for an open estate and PR information (search your county courts).

Helpful Hints

Start by confirming how title was held — joint tenancy vs tenants in common changes who must be joined.
Search probate records early. If a personal representative exists, naming that person avoids chasing multiple heirs.
Document every effort to locate missing heirs — the court will expect proof before allowing service by publication.
If minors or incapacitated persons have an interest, request a guardian ad litem quickly so their rights are protected and the case can proceed.
Consider a quiet title or declaratory judgment alongside partition if ownership shares are in dispute.
Keep records of family relationships (birth certificates, wills, marriage certificates) — these speed heirship determinations.
Talk to a real property attorney in your county — partition and probate issues are technical; counsel can handle service, joinder, and court filings correctly.

Disclaimer: This article explains general Missouri legal principles about partition and heirs. It is educational only and is not legal advice. For advice about your specific situation, consult a licensed Missouri attorney who can evaluate your facts and represent you in court.