What Secretary of State paperwork will a bank accept to prove someone was the sole member of an Illinois LLC?

Short answer: A bank will typically want a certified copy of the LLC’s formation record (Articles of Organization) or a Certificate of Status from the Illinois Secretary of State, together with the LLC’s signed operating agreement (if one exists) and proof of the member’s death. If the member was the sole owner, the bank usually also requires probate or other court paperwork (for example, Letters of Office, Letters Testamentary, or a court order naming a personal representative) before it will change account ownership or release funds. Some banks will accept additional documentation such as a certified copy of the death certificate plus a signed assignment or affidavit — but banks set their own requirements, and many will not act without probate authority.

Detailed answer — what to get from the Illinois Secretary of State and why

Banks rely on documentary proof that shows (1) the LLC existed and (2) who had authority over the LLC. The Illinois Secretary of State (SOS) can provide documents that satisfy item (1). Documents that commonly come from the SOS and that banks accept include:

Certified copy of the Articles of Organization (or the filed formation documents) — these are the LLC’s original filing with the Illinois SOS and prove the LLC was formed under Illinois law. The articles show the official name and filing history. Note: Illinois formation filings usually do not list every member. They establish the company, not full ownership details.
Certificate of Status (often called a Certificate of Good Standing) — this certificate shows the LLC is, or was, an active Illinois entity in good standing on a particular date. It confirms the SOS’s recorded existence of the LLC.
Copies of any filed amendments — if the LLC filed amendments that changed management structure or named a manager, those filings give the bank additional evidence about who had authority to act for the company.
Record of registered agent and principal office — SOS records will confirm the registered agent and the company’s last known principal address, which helps corroborate identity of the company.

You can search and order certified copies or Certificates of Status from the Illinois Secretary of State’s Business Services pages and the Online Business Services portal. See the SOS Business Services main page: https://www.cyberdriveillinois.com/departments/business_services/home.html.

Why SOS documents alone are often not enough

Secretary of State filings confirm that the LLC existed and the public-facing details of the entity. They usually do not list all members or spell out succession rules for membership. That is why banks also want:

The operating agreement — this internal document often identifies members, states whether the LLC is member-managed or manager-managed, and explains what happens to a member’s interest after death. The operating agreement is not filed with the SOS but it is the primary document for proving who owned and who can act for the LLC.
Evidence of the member’s death — a certified copy of the death certificate.
Probate or court authority — most banks require Letters Testamentary (if there is a will) or Letters of Office/Administration (if there is no will), or a court order that gives a named person authority to administer the decedent’s estate or to act for the LLC. This gives the bank legal authority to release funds or transfer memberships.
Assignment, resolution, or membership-transfer documentation — if the operating agreement provides for an automatic transfer (for example, to a named beneficiary) or if the estate administrator signs an assignment of the membership interest, the bank will want those signed, notarized papers.

Relevant Illinois statutes and resources

Illinois Limited Liability Company Act, 805 ILCS 180/ (general source for governing rules on LLCs and membership interests): https://www.ilga.gov/legislation/ilcs/ilcs3.asp?ActID=1463&ChapterID=33. The Act explains formation, management structure, and member/manager rights (see the Act text for details about membership transfers and governance).
Illinois Probate Act, 755 ILCS 5/ (general source on appointment of personal representative and probate procedures): https://www.ilga.gov/legislation/ilcs/ilcs3.asp?ActID=2106&ChapterID=61. Probate paperwork (Letters) usually give the personal representative the power banks require to access decedent assets, including LLC membership value.
Illinois Secretary of State — Business Services (for entity search, ordering certified copies, and obtaining a Certificate of Status): https://www.cyberdriveillinois.com/departments/business_services/home.html.

Practical step-by-step checklist

Run an SOS business search for the LLC name and order a certified copy of the Articles of Organization and a Certificate of Status from the Illinois SOS.
Collect the LLC’s operating agreement and any amendments. If you can’t find it, note that many banks will refuse to alter account signers without it.
Get a certified copy of the member’s death certificate from the county vital records office.
Open probate or obtain appointment paperwork. If the decedent left a will, the executor should get Letters Testamentary. If there is no will, the court will appoint an administrator and issue Letters of Office. Provide the bank with those letters or a court order authorizing the representative to act for the estate or the LLC.
Provide any LLC-specific documents showing succession (for example, an operating agreement clause, written assignment of membership, or a member resolution). Have these documents notarized if requested by the bank.
Bring the bank certified SOS documents, the operating agreement, the death certificate, and the probate papers in person with photo ID for the person presenting them. Ask the bank in advance what combination of documents they require.

Alternatives and special situations

If the LLC was truly a single-member disregarded entity for tax and the bank account was in the decedent’s personal name, the bank may treat the account as part of the estate rather than an LLC account.
Some banks permit a short-form affidavit or a small-estate procedure for low-value accounts. Illinois has streamlined small estate processes in some situations, but eligibility, limits, and bank acceptance vary. Check the Illinois Probate Act and ask the bank and a probate attorney.
If the operating agreement included an express transfer-on-death or named successor, provide that paperwork. It may avoid formal probate for the LLC interest, but banks still often want proof the successor has legal authority to withdraw funds.

Helpful hints

Call the bank first. Ask exactly which documents they need and whether they must be original or certified copies.
Order certified copies from the Illinois Secretary of State — banks prefer certified documents over photocopies or screenshots of online records.
Bring the LLC’s operating agreement. If you can’t find it, ask other family members, the decedent’s attorney, or the business’s accountant.
Expect banks to require probate paperwork in most solo-member-death situations. Plan for the probate timeline unless the bank expressly allows a different process for small accounts.
Keep originals of everything, and store copies in multiple safe places. Banks usually keep copies but may require originals at first review.
When in doubt, consult a probate or business-transaction attorney in Illinois. They can prepare the exact documents banks typically accept and, if necessary, obtain court orders to compel a bank to release funds.

Disclaimer: I am not a lawyer and this is not legal advice. This article explains common practices and Illinois statutes you may find relevant. Each bank has its own requirements, and the correct paperwork depends on the LLC’s operating agreement and whether probate is opened. For advice tailored to your situation, consult a licensed Illinois attorney who handles probate and business law.