Short answer: The Washington Secretary of State can provide certified copies of the LLC’s formation filing (Certificate of Formation/Articles), any filed amendments, and a Certificate of Status (good standing). Those documents prove the LLC exists and who filed or managed it for public record purposes, but they usually do not show private ownership (the membership interest). To prove that a deceased family member was the sole member, banks commonly require those SOS-certified records plus the LLC’s internal documents (operating agreement, membership certificates or resolutions) and probate or estate paperwork (death certificate and letters testamentary or administration).

Detailed answer — what the Secretary of State can provide and what banks typically want

Under Washington law, the Secretary of State maintains public records of business entity filings, including the LLC’s initial formation document and subsequent filings. You can order certified copies of those records from the Washington Secretary of State to show the LLC’s legal existence and any publicly filed changes.

• Certificate of Formation / Articles of Organization (certified copy): This is the document the LLC files to be created. A certified copy from the Secretary of State proves the LLC was legally formed.
• Filed amendments or merger documents (certified copies): If the LLC changed its name, membership structure (if publicly amended), or merged, those filings will be on record and can be certified.
• Certificate of Status / Certificate of Good Standing: The Secretary of State can issue a certificate that the LLC is currently registered and has filed required reports. That helps a bank confirm the entity’s active status.
• Annual report filings and registered agent details: Annual reports and registered agent information are public and can be downloaded or certified from the SOS record. These typically do not list members.

You can start at the Washington Secretary of State’s business division for searches, copies, and certified documents: https://www.sos.wa.gov/corps/.

Important limitation — membership is generally not a public SOS record

The Secretary of State maintains filings that create and register the LLC, but most states — including Washington — do not require the SOS to record private ownership lists (member lists) or operating agreements. For Washington LLC law, see the Revised Code of Washington (RCW) chapter on limited liability companies: https://app.leg.wa.gov/rcw/default.aspx?cite=25.15. That chapter governs formation, management, and member rights, but ownership details typically remain in the LLC’s internal records rather than in SOS public filings.

What banks commonly require to accept a claim that your relative was the sole member

Banks must follow their own risk and compliance rules (and federal regulations) before releasing funds or changing account signers. Typical documentation banks request includes some combination of:

1. SOS certified documents: Certified Certificate of Formation (or certified Articles), certified amendments, and a Certificate of Status/Good Standing.
2. LLC internal documents: The signed operating agreement, any membership certificates, member resolutions, or written statements identifying the sole member. These documents usually show who owned the membership interest.
3. Proof of death and authority: Certified death certificate for the member and a document showing who now has legal authority to act for the member or the member’s estate — for example, letters testamentary or letters of administration issued by a probate court.
4. Probate or small-estate documents: If the estate has an appointed personal representative (executor/administrator), banks typically accept the court-issued letters. If the estate qualifies as a small estate under Washington law, some banks will accept a small estate affidavit if permitted under RCW probate rules.
5. IRS/EIN records: Bank may request proof of the LLC’s Employer Identification Number (EIN) and recent tax records, which often align with the operating agreement and ownership claims.

If you cannot produce an operating agreement or membership certificate (these are internal documents), the bank may require a probate court order recognizing the claimant’s authority over the LLC interest or an affidavit from an authorized representative. In many cases, banks refuse to release funds until they see either (a) the LLC’s incontrovertible internal evidence of sole ownership or (b) a probate court document assigning authority.

Practical steps to prepare the paperwork

1. Search the SOS records for the LLC and order certified copies of the Certificate of Formation and any amendments and a Certificate of Status: start at https://www.sos.wa.gov/corps/.
2. Locate the LLC’s operating agreement, membership certificates, or member resolutions. If you find them, get certified copies or notarized true copies.
3. Obtain a certified copy of the death certificate from the vital records office.
4. If the estate has opened probate, request certified Letters Testamentary or Letters of Administration from the probate court. Washington probate statutes are in Title 11 of the RCW: https://app.leg.wa.gov/rcw/default.aspx?cite=11.
5. Talk to the bank in advance. Ask which specific documents they will accept to change account ownership, close accounts, or release funds. Banks differ in their internal policies.
6. If documents are missing or the bank insists on a court order, consult a probate or estate attorney to obtain the necessary court documents or advice on small-estate procedures.

When you will likely need a court order

If the LLC’s internal documents are missing, ambiguous, or if multiple claimants assert ownership, the bank will often require a probate or court order recognizing who holds the membership interest or who has authority to manage or liquidate LLC assets. An attorney can help you petition the probate court for a declaration of rights or for appointment as personal representative so you can access the LLC’s funds.

Helpful hints

• Order certified SOS copies — banks prefer certified originals rather than photocopies.
• Bring the death certificate and any probate letters together with the SOS records and the LLC’s internal documents when you visit the bank.
• If the LLC’s operating agreement names a successor manager or transfer procedure upon death, point the bank to that clause; it often solves the problem without probate.
• Contact the bank’s business accounts or legal-department desk before your appointment to get a document checklist.
• If the bank refuses, ask in writing what additional documents they require; that written list helps your attorney or the probate court respond efficiently.
• Consider hiring an attorney experienced in Washington probate and business-entity matters if you run into disputes or missing records.

Where to get the SOS and statute resources

Washington Secretary of State (Business & Corporations): https://www.sos.wa.gov/corps/

Washington LLC statute (RCW chapter 25.15): https://app.leg.wa.gov/rcw/default.aspx?cite=25.15

Washington probate statutes (Title 11 RCW): https://app.leg.wa.gov/rcw/default.aspx?cite=11