Short answer
A MyTax Illinois Letter ID is a code of letters and numbers that the Illinois Department of Revenue (IDOR) uses to identify each letter it sends. You enter it to activate a MyTax Illinois logon for an individual income tax account. The letter must be from the last 90 days. If you have filed before but have no recent letter, choose “Request a Letter ID,” and IDOR mails one to the address it has on file.
Key takeaways
- IDOR says a Letter ID is “a unique set of alpha and numeric characters used to identify each letter issued by IDOR.”
- The Letter ID activates a MyTax Illinois logon for an Individual Income Tax account. IDOR says the letter must have been “issued within the last 90 days.”
- Common letters that work include a Return Correction Notice, a Notice of Tax Due, and a Notice of Deficiency. Identity Verification letters (LTR-425-C, LTR-425-D, and LTR-425-Q) cannot be used to create a logon.
- If you have no recent letter, select “Request a Letter ID” on the Individuals panel. IDOR says it will send the letter “to the mailing address we have on file for you,” and that it “can take up to 10 days to receive.”
- Requesting a Letter ID needs an IL-PIN, the account number IDOR assigns after you file an Illinois individual income tax return. First-time filers are not issued an IL-PIN.
- Business accounts do not use a Letter ID to activate a logon. IDOR lists an owner or officer Social Security Number, a PIN issued by IDOR, or account activity validation instead.
What a MyTax Illinois Letter ID is
MyTax Illinois is the online account system of the Illinois Department of Revenue (IDOR). IDOR describes it as a place to “file returns, renew licenses, register accounts, make payments, review correspondence, and other account management options.” Most of those features need a logon.
The Letter ID is how an individual taxpayer proves that the account is theirs. IDOR’s MyTax Illinois help page says: “A Letter ID is a unique set of alpha and numeric characters used to identify each letter issued by IDOR.” The same page says that to get access to an Individual Income Tax account, “you are required to enter a Letter ID from a letter that was issued within the last 90 days from your Individual Income Tax account.”
The code is tied to one letter. Each new letter from IDOR has its own Letter ID. IDOR’s letters page says to activate your account “within 90 days of the date on your letter or notice.” After that, “you will be required to request a new Letter ID to activate your account.”
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Where to find your Letter ID
The Letter ID is printed on letters and notices IDOR mails to you. IDOR’s letters page says “You may use most letters sent from IDOR to create a new logon.” The help page lists common letters that can be used to activate a logon.
The IDOR pages we read on October 25, 2026, do not say where on the page the Letter ID is printed. They also do not show a sample of its exact format. Read the whole letter and look for the words “Letter ID.” Check the date on the letter too, because the 90-day window runs from that date.
| Letter | Can it activate a MyTax Illinois logon? |
|---|---|
| Return Correction Notice | Yes, listed by IDOR as a common letter you can use |
| Notice of Tax Due | Yes, listed by IDOR as a common letter you can use |
| Notice of Deficiency | Yes, listed by IDOR as a common letter you can use |
| Notice before Collection | Yes, listed by IDOR as a common letter you can use |
| Examiner’s Report | Yes, listed by IDOR as a common letter you can use |
| Notice of Proposed Tax Due | Yes, listed by IDOR as a common letter you can use |
| Certain IDOR Collections notices | Yes, listed by IDOR as a common letter you can use |
| Identity Verification letters (LTR-425-C, LTR-425-D, LTR-425-Q) | No. IDOR says these “cannot be used to create a MyTax Illinois logon.” |
From IDOR’s Creating a Logon help page and its Letters and Notices for Individual Income Tax page, read on October 25, 2026. The letter must be from the last 90 days.
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What the Letter ID is used for
The main use is activating a MyTax Illinois logon for an Individual Income Tax account. With a logon, IDOR says you can file returns and view your correspondence. IDOR’s letters page also says you can use MyTax Illinois “to check your account balances or view any notices sent to you.”
A second use is answering an identity verification letter online. IDOR’s identity verification page says to go to MyTax Illinois, select the Identity Verification Documents link, “enter your Letter ID, and follow the instructions.” The page adds: “if you do not have a Letter ID, you must submit your documents by mail.”
Some tasks do not need a logon. IDOR’s help page answers “No” to the question of whether you must activate a logon to file your current year Form IL-1040. IDOR also says a logon is not required to make an individual income tax payment, check a refund, or look up your IL-PIN.
Joint filers
IDOR’s help page says that for joint filers, “the Letter ID will only activate a logon for the taxpayer listed first on the letter (i.e., the primary spouse).” Activate the logon under the primary taxpayer.
How to request a new Letter ID
If you have no letter from the last 90 days, you can ask IDOR to mail one. IDOR’s help page says to select “Request a Letter ID” on the Individuals panel of MyTax Illinois. The same page says “You must have previously filed a tax return with IDOR in order to activate a logon.”
The request needs an IL-PIN. IDOR’s answer page says “The IL-PIN is the account number we assign after you have filed an Illinois individual income tax return.” The same page says the IL-PIN is required to “request a Letter ID.” First-time filers with Illinois are not issued an IL-PIN.
IDOR mails the new letter. The help page says “We will send a letter to the mailing address we have on file for you.” IDOR’s MyTax Illinois page says the Letter ID “can take up to 10 days to receive.” The pages we read give no other delivery estimate.
- 1Find your IL-PIN with the IL-PIN Inquiry in MyTax Illinois. IDOR says you can look it up with your Illinois driver’s license, Illinois state ID, or the adjusted gross income (AGI) from your most recently filed Illinois return.
- 2Check that the mailing address IDOR has for you is current. The new letter goes to that address.
- 3Select “Request a Letter ID” on the Individuals panel of MyTax Illinois.
- 4Wait for the letter. IDOR says it can take up to 10 days to receive.
- 5Use the Letter ID to activate your logon within 90 days of the date on the letter.
Which address the Letter ID goes to, and how to change it
A requested Letter ID only reaches you by mail, at the address IDOR has on file. If that address is old, the letter goes to the old address.
Mail forwarding may not help. IDOR’s answer page says: “Be aware that most mail from us is not forwarded by the US Postal Service, even if you have a forwarding address.” IDOR says it does this to protect you. Our guide on how long USPS forwards mail explains how forwarding works in general.
IDOR gives three ways to update an individual income tax address. If you have not yet filed, “your address will be automatically updated when you file your Form IL-1040 or IL-1040-X.” You can also update it in a MyTax Illinois account. If you have already filed, IDOR says you may call 800 732-8866 “to update the address while verifying tax information from your account with a representative.”
The online route has a limit. IDOR says that to create a MyTax Illinois account, “you must have a recent bill or notice from the Illinois Department of Revenue.” So if you have no recent letter and IDOR has an old address, the phone route may be the practical first step. IDOR says to call “with a copy of your previously filed IL-1040 or with a notice you received.”
How business accounts log on and update their addresses
Business logons work differently. IDOR’s help page says that to activate a logon for a business, you can use an “Owner/Officer or Responsible Party Social Security Number,” a “PIN previously issued by IDOR,” or “Account Activity validation.” A Letter ID is not on that list. IDOR also says to “Allow 24 hours from your registration confirmation email before activating a logon.”
The business tax ID is the Illinois Account ID. IDOR’s registration guide says the confirmation email lists “the tax types for which we have you registered” and “the corresponding account numbers.” Your Certificate of Registration is in MyTax Illinois under “View more account options” and then “View Account Letters.”
A business can have more than one address on file. IDOR’s answer page says its system allows “a corporate legal address, site address (Illinois locations only), general mailing address, and tax-specific mailing addresses.” The page says to be specific about which one you need changed. You can update them in MyTax Illinois, with Form REG-3-C, or by calling Central Registration at 217 785-3707.
IDOR’s registration page lists what can go wrong if you do not update. It says “your returns and payments may not be processed correctly” and “we may send you a tax bill or notice.” The IDOR address is separate from your state business filings. Our guide to an Illinois LLC not in good standing covers the Secretary of State side.
Choosing an address where IDOR mail gets read
IDOR sends the Letter ID, notices, and bills by mail. Use a mailing address where you will see tax mail soon after it arrives. Georgia also mails a Letter ID, and our guide to the Georgia Tax Center Letter ID explains how Georgia handles it.
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Not legal or tax advice
This guide summarizes the Illinois Department of Revenue pages cited here, as read on October 25, 2026. MyTax Illinois screens and letters change from time to time. Contact IDOR about your account, and ask an Illinois tax professional about your filing.
Frequently Asked Questions
Sources & References
Primary sources this guide is based on.
- 1Illinois Department of Revenue · Creating a Logon, MyTax Illinois Help (accessed October 25, 2026)
- 2Illinois Department of Revenue · What is MyTax Illinois and how do I access it? (accessed October 25, 2026)
- 3Illinois Department of Revenue · Letters and Notices for Individual Income Tax (accessed October 25, 2026)
- 4Illinois Department of Revenue · What is an IL-PIN? (accessed October 25, 2026)
- 5Illinois Department of Revenue · How do I change my address for individual income tax? (accessed October 25, 2026)
- 6Illinois Department of Revenue · How do I update my business registration information? (accessed October 25, 2026)
- 7Illinois Department of Revenue · Identity Verification Letters Information (accessed October 25, 2026)
- 8Illinois Department of Revenue · MyTax Illinois Functions (accessed October 25, 2026)
- 9Illinois Department of Revenue · PIO-117, How to Register your Illinois Business (accessed October 25, 2026)
- 10Illinois Department of Revenue · Business Registration (accessed October 25, 2026)
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