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FousMyTax Illinois

Get your MyTax Illinois returns and letters through an API

Read your submitted returns, IDOR letters and account period balances from MyTax Illinois with one API call each. A workflow can check View Letters every weekday morning and email you each new letter with its Letter ID and tax account.

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Works with your own MyTax Illinois account. Fous is an independent product.

What you can build on MyTax Illinois

  • Get submitted returns

    Build this

    Reads Manage Payments and Returns with Show set to Returns: each return filed for a tax account, its period, status and confirmation number.

    Takes
    Tax account, period (optional)
    Returns
    Return type, tax account, period, submitted date, status, confirmation number

  • List IDOR letters

    Build this

    Reads the Letters tab under More, then View Letters: the copies of correspondence IDOR mailed to you, with each letter's Letter ID and date.

    Takes
    Mailed since (optional)
    Returns
    Letter ID, letter name, tax account, period, date mailed

  • Get account periods and balances

    Build this

    Opens View more account options for one tax account, then View Account Periods under Periods and Submissions, and reads each period with its balance.

    Takes
    Tax account
    Returns
    Tax account, period end date, balance

  • Pay a period by bank account debit

    Build this

    Opens a period in View Account Periods, selects Make a Payment and Bank Account Debit, enters the amount and date and submits the payment.

    Takes
    Tax account, period end date, payment type, amount, payment date
    Returns
    Confirmation number, tax account, period, amount, payment date, status

Automate MyTax Illinois with a workflow

A workflow runs your methods as one process, with nobody at the screen. A schedule or a call from your own system starts it, the steps run in order, and the result arrives in your inbox or in the systems you already use.

  • New IDOR letters, every weekday

    Build this
    Starts
    Every weekday at 8:00 Central time
    Step 1
    List the letters on the Letters tab under View Letters.
    Step 2
    Keep the letters that were not there on the last run.
    Step 3
    Email you each new letter's Letter ID, name, tax account, period and date mailed.

  • Returns still Pending after a day

    Build this
    Starts
    Every weekday at 9:00 Central time
    Step 1
    For each tax account you name, get the submitted returns.
    Step 2
    Keep the returns still Pending that were submitted before today.
    Step 3
    Post tax account, return type, period, submitted date and confirmation number to your webhook.

  • Monthly balance check across tax accounts

    Build this
    Starts
    Monthly on the 1st at 7:00 Central time
    Step 1
    For each tax account you name, get the account periods and their balances.
    Step 2
    Keep the periods with a balance other than zero.
    Step 3
    Email you one list grouped by tax account, with period end date and balance.

You can run a workflow by hand on every plan, Free included. Schedules and webhook triggers come with the paid plans, from $29 a month.

Once built, one call from your code

Once you have built a method, it is one POST to /v1/runs from your backend, or a tool an AI agent calls over MCP. This is what “Get submitted returns” would look like.

Example request
curl https://api.fous.com/v1/runs \
  -H "Authorization: Bearer $FOUS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "method": "mytax.illinois.gov/get_submitted_returns",
    "input": {
      "tax_account": "Sales & Use Tax",
      "period": "2026-10"
    }
  }'
Example response
{
  "status": "completed",
  "data": {
    "tax_account": "Sales & Use Tax",
    "returns": [
      {
        "return_type": "ST-1",
        "tax_account": "Sales & Use Tax",
        "period": "2026-10",
        "submitted_date": "2026-11-11",
        "status": "Pending",
        "confirmation_number": "0-482-913-570"
      }
    ]
  }
}

An example with invented data, not a ready-made endpoint. The method exists in your organization once you build it, and its name, inputs and fields follow your request.

MyTax Illinois’s own options

IDOR describes electronic filing programs for software, not an API for reading a MyTax Illinois account. ST-1 and ST-2 returns can be sent from your own or approved software, and withholding returns through FSET, both after enrollment on MyDevPortal and testing. Letters, balances and submissions are read in MyTax Illinois, which is free.

OptionWhat it coversWhat it takes
Sales and use tax electronic filingForms ST-1 and ST-2 sent from your own software or from an approved third-party software vendor.The Business Electronic Filing Enrollment Application on MyDevPortal, then testing with IDOR. Build to implementation guide STS-81.
FSET for withholdingIL-941 and IL-941-X returns and payments for large employers and payroll companies.Enrollment on MyDevPortal, a Letter of Intent, then testing. Reporting agents need Form IL-8655 from each client.
Submit Bulk W2/1099 FileW-2 and 1099 forms filed in bulk from the MyTax Illinois home page, without a logon.A bulk W-2 or 1099 file, submitted from the Non-Login Return or Report panel.
MyTax Illinois by handFiling returns, making payments, reading letters and viewing account periods.A free MyTax Illinois logon for a registered business.

Read on November 12, 2026: Sales and use tax electronic filing, Withholding and unemployment insurance (FSET), MyTax Illinois functions.

Signing in to MyTax Illinois

MyTax Illinois signs you in with a username and password, or a passkey, then a two-step verification code sent by email, text message or an authenticator app. You choose a primary and a backup method, and a trusted browser can skip the code. With Fous you sign in once through MyTax Illinois's own sign-in: the login is sealed with AES-256, emailed codes are handled and an expired session is signed back in.

Worth knowing

Requests are processed once a day
A submitted return or payment shows Pending until IDOR processes it, usually once a day, then Completed. A balance can take up to five business days to update after a payment.
Only a pending payment can be cancelled
A return can be withdrawn from Submissions, then edited or deleted. A payment cannot be edited, and it can be cancelled only while its status is pending.
Business income tax returns are filed elsewhere
Business income tax returns cannot be filed or amended in MyTax Illinois. You can still pay a period there, through View Account Periods and Make a Payment.
The Master logon controls other users
The Master logon holder decides whether additional logons are allowed and creates them. Third-party access is granted under Manage third party access, and is not available for accounts administered by IDES.

More in Government: US state and local tax

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Frequently asked questions

Not for reading an account. IDOR runs electronic filing programs for software: ST-1 and ST-2 through the sales and use tax program, and IL-941 through FSET, both after enrolling on MyDevPortal and testing. Letters, balances and submissions are read in MyTax Illinois itself.

Yes, through third-party access or an additional logon. Third-party access is granted under Manage third party access, and the Master logon holder creates additional logons. Third-party access is not available for accounts administered by IDES.

Under More, then View Letters. The Letters tab holds copies of correspondence IDOR mailed to you, each with its own Letter ID. Messages are separate one-way notices you cannot reply to.

Yes, after enrolling and testing. You complete the Business Electronic Filing Enrollment Application on MyDevPortal and build to STS-81, which describes ST-1 version ST1V6.0 for January 2026 periods and later. You can also buy software from an approved vendor.

No. Fous is an independent product. You use it with your own MyTax Illinois logon, and a method reads and does only what that logon can.

Put MyTax Illinois behind an API call

Describe one job in Studio and see the method it builds, with 100 credits a month and no credit card, or book a demo and bring the sites your team signs in to.

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Fous is an independent product: it is not affiliated with, endorsed by or sponsored by the operator of MyTax Illinois (Illinois Department of Revenue). The name is used only to say which system this page is about. Something here wrong or out of date? Write to legal@fous.com.