Detailed Answer

Short answer: Yes. Under Idaho law, heirs of a deceased co-owner (such as a sibling) who inherit an ownership interest must be included in a partition action. To add them you generally identify the heirs, amend or substitute parties in the pending case, properly serve the heirs (or publish notice if their identities/addresses are unknown), and, when needed, ask the court to appoint a guardian ad litem for minors or unknown claimants.

Why heirs must be included in a partition action (Idaho)

A partition action divides or sells property owned by two or more persons so each owner receives their share. The court can only partition property if it has jurisdiction over every person who holds a legal or equitable interest in the property. If a co-owner died, that co-owner’s interest typically passes to their heirs or devisees under probate or by intestacy. Those heirs have legal rights that affect the property, and the court must join them so the partition order resolves title for everyone.

How to identify who to add

Check the deed and county land records to confirm the deceased co-owner and the recorded title interests.
Search probate records in the county where the deceased lived. If probate was opened, the personal representative’s filings, will, or final decree show heirs/devisees.
If no probate exists, identify heirs under Idaho intestacy rules (heirs usually include spouse, children, parents, siblings, etc.). You can check Idaho’s probate statutes and local court filings to confirm. Useful resource: Idaho Legislature statutes index: https://legislature.idaho.gov/statutesrules/idstat/
Use public records, obituary notices, and county assessor/recorder data to find current addresses for heirs.

Step-by-step: how to add heirs to an existing partition action in Idaho

Collect proof of the co-owner’s death. Obtain a certified death certificate and the deed showing their ownership interest.
Determine heirship. Check whether a probate case exists. If yes, use probate filings to identify heirs. If no probate, prepare an heirship affidavit or investigation to determine probable heirs.
File a motion or amended complaint to join or substitute parties. Idaho procedure allows you to bring new parties into an action by amendment or by substitution when a party dies. If the original defendant/co-owner died, the court typically allows substitution of the successor(s) in interest (the heirs). Be prepared to explain the basis for joinder and provide supporting documents.
Serve the heirs properly. If you know their names and addresses, serve them with the complaint or amended pleading according to Idaho service rules (personal service, certified mail, etc.). If heirs are unknown or cannot be located despite diligent effort, you may seek court permission for substituted service or publication of notice. Check local court rules for publication procedures.
Ask the court to appoint a guardian ad litem if necessary. If an heir is a minor or legally incapacitated, request appointment of a guardian ad litem to represent that person’s interests in the partition action.
Provide the court with title documents. Bring deeds, death certificate, probate filings (if any), and any affidavits of heirship to prove who holds the interest.
Request an order naming all owners and authorizing partition. Once heirs are joined, the court can proceed to divide the property physically or order sale and distribution of proceeds according to ownership shares.

Service, publication and unknown heirs

If an heir cannot be found after reasonable search, Idaho courts permit service by publication or other court-ordered methods to give notice to unknown or absent parties. The court will typically require an affidavit describing the search and may set deadlines for someone to appear. If no one appears, the court can proceed and eventually distribute the proceeds, subject to later claims by anyone who later proves an entitlement.

Minors and incapacitated persons

When an heir is a minor or incompetent, Idaho courts usually require appointment of a guardian ad litem or a guardian for that person’s interest before the court orders partition or disbursement of proceeds. This step protects the minor’s or incapacitated person’s legal rights.

Key documents and evidence to prepare

Certified death certificate for the deceased co-owner.
Recorded deed(s) showing ownership and legal description.
Probate case filings (if probate was opened): petition, letters, inventory, decree of distribution, etc.
Affidavit of heirship or genealogical evidence if no probate exists.
Affidavits proving attempts to locate missing heirs (for publication requests).
Title searches and county assessor parcel information.

Timing, costs, and practical considerations

Adding heirs may delay a partition, especially if heirs are numerous, out of state, unknown, or minors. Service by publication lengthens case time and increases cost. Courts may appoint commissioners to value and divide property—those fees and costs come from the estate or partition proceeds. Consider cost-benefit: sometimes an estate or family resolves ownership by agreement outside court to avoid litigation costs.

When to consult an attorney

Consult an Idaho real property or probate attorney if:

Heirs are unknown or difficult to locate.
There is disagreement about who the heirs are.
Minors or incapacitated persons are involved.
Title is complex (lien claims, trusts, prior deeds, or adverse possession issues).

An attorney can file the correct motions, prepare proof of heirship, coordinate service or publication, and represent interests at hearing.

Resources: Idaho courts information and local rules are available at the Idaho Judicial Branch website: https://www.idcourts.us/. For Idaho statutes and code sections relevant to probate, actions and property, see the Idaho Legislature’s statutes page: https://legislature.idaho.gov/statutesrules/idstat/.

Disclaimer: This article explains how partition and joinder of heirs commonly work in Idaho. It is informational only and not legal advice. For advice about a specific case, consult a licensed Idaho attorney.

Helpful Hints

Start with the deed and county recorder: that tells you who owned the property and which county to search for probate records.
Search probate records where the deceased lived—probate filings often identify heirs and a personal representative.
Document your efforts to find missing heirs—courts want to see diligence before allowing service by publication.
Consider a title search early to reveal liens or other claimants before filing for partition.
If heirs agree, a written settlement dividing proceeds or conveying interests can avoid court; record any agreement with the county recorder.
When minors are involved, ask the court about protective deposit or blocked account procedures for their share rather than releasing funds directly.
Keep communication records with heirs—email, certified mail receipts, and affidavits help show service attempts.