How to File an Illinois Sales Tax Return on MyTax Illinois

To file an Illinois sales tax return, submit Form ST-1 through the MyTax Illinois portal at mytax.illinois.gov, reporting your gross receipts, subtracting nontaxable sales on Schedule A, and paying the tax you collected to the Illinois Department of Revenue (IDOR).1Illinois Department of Revenue. ST-1 Sales and Use Tax and E911 Surcharge Return The return is due by the 20th of the month after your reporting period ends. File and pay on time and you keep a small retailer’s discount; miss the deadline and penalties start right away.

What To Gather Before You Log In

Pull your numbers for the period first. You need total gross receipts from all retail sales, which is where the ST-1 begins. From there you subtract nontaxable transactions on Schedule A — sales for resale, sales to exempt organizations, and similar items — to reach your net taxable amount.2Illinois Department of Revenue. ST-1 Sales and Use Tax and E911 Surcharge Return

Each deduction needs documentation behind it. For resale exemptions, that means a completed resale certificate from the buyer. For sales to exempt organizations, you need the buyer’s exemption identification number. If IDOR audits you and the paperwork is not there, the deduction gets disallowed and you owe the tax plus interest.

You also need to know which rate applies to each sale. The general state rate is 6.25 percent on most merchandise; qualifying drugs and medical appliances are taxed at 1 percent.3Illinois Department of Revenue. What Are the Retailers Occupation and Use Tax Rates in Illinois Local taxes from home-rule municipalities, counties, and special districts sit on top of the state rate, so the combined rate depends on where the sale takes place. MyTax Illinois handles much of the calculation, but you still have to categorize your receipts correctly by location and type.

Keep the underlying records. Illinois law requires retailers to keep books, invoices, bills of sale, and inventory records, with enough detail on nontaxable transactions to show the customer, date, nature, and amount.4Illinois General Assembly. Illinois Code 35 ILCS 120/7 – Retailers Occupation Tax Act Six years is a safe retention window because IDOR’s audit lookback extends that far when taxable receipts are underreported by more than 25 percent.

When Your Return Is Due

IDOR assigns your filing frequency based on your average monthly tax liability. You do not pick it; IDOR notifies you if it needs to change.5Illinois Department of Revenue. Filing, Payment, and Refund Resources for Illinois Retailers

Whatever your frequency, the return is due by the 20th of the month after the reporting period ends.7Illinois General Assembly. Illinois Code 35 ILCS 120/3 – Retailers Occupation Tax Act A January monthly return is due February 20. A first-quarter return covering January through March is due April 20. If the 20th lands on a weekend or holiday, you have until the next business day.

Filing Through MyTax Illinois

Many Illinois retailers are required to file electronically, and if you are under that mandate without a waiver, electronic filing is the only way to qualify for the retailer’s discount.8Illinois Department of Revenue. ST-1 Instructions Even if you are not mandated, MyTax Illinois is the simplest route.

Log in at mytax.illinois.gov. From the dashboard, select Sales and Use Tax to see your open filing periods, then click the period you are filing for. The portal opens the digital ST-1.

Enter your gross receipts on Step 1, then work through Schedule A to subtract your nontaxable deductions. Many fields auto-calculate once you enter the base data, but double-check the location-specific information because it drives how local tax gets allocated to the right municipality.

Review the calculated totals on the summary screen. When you are satisfied, click Submit. The system generates a confirmation number. Save it. That number is your proof of timely filing if a dispute comes up later.

Pay in the same session. MyTax Illinois accepts ACH debit, which pulls funds directly from your bank account, and credit card payments. You can also print a voucher and mail a check, but a mailed payment must be postmarked by the due date. Most filers use ACH debit because it clears immediately and removes any question about postal timing.

If You Sell From More Than One Location

Operating one business from multiple Illinois sites means attaching Form ST-2, the Multiple Site Form, to your ST-1.8Illinois Department of Revenue. ST-1 Instructions Each location likely has a different combined rate because of local taxes, and ST-2 allocates receipts and tax collected to each specific site. You can file it through MyTax Illinois alongside the ST-1. Getting the breakdown wrong is one of the faster ways to trigger correspondence from IDOR, because municipalities watch their local tax revenue closely.

Keeping the Retailer’s Discount

Illinois lets retailers keep a portion of the sales tax they collected as a reward for filing and paying on time. You must file the ST-1 and pay the full amount due by the deadline. If you are required to file electronically and have no waiver, only an electronic filing counts.9Illinois Department of Revenue. As a Retailer, Am I Allowed a Discount From the Sales Tax I Report On My Return

For returns due on or after January 1, 2025, the discount is capped at $1,000 per month under Public Act 103-592. File even one day late or short-pay the tax and you lose the discount entirely for that period. There is no partial credit. A monthly filer who stays current can keep up to $12,000 across a full year, so the deadline is worth protecting.

What Happens If You File Late

The late-filing penalty under the Illinois Uniform Penalty and Interest Act runs in two tiers:

First-time offenders catch a break. If the failure is non-fraudulent and you have not missed a deadline in the prior two years, IDOR will abate the penalty. Abatement happens after assessment, though, so you may need to request it.

Interest accrues from the day after payment was due. Illinois uses simple interest at the federal underpayment rate under Internal Revenue Code Section 6621, calculated daily until paid, with the rate reset every January 1 and July 1.11Illinois Department of Revenue. Pub-103, Penalties and Interest for Illinois Taxes Late-filing and late-payment penalties stack. They do not merge or offset.

Fixing a Mistake After You File

If you spot an error after submitting, file Form ST-1-X, the Amended Sales and Use Tax and E911 Surcharge Return, with one ST-1-X per reporting period you are correcting.12Illinois Department of Revenue. ST-1-X Instructions If your original return included ST-2 for multiple locations, file ST-2-X too. If Schedule A deductions need correcting, attach Schedule A-X. Skip these companion forms and IDOR will delay processing or reject the amendment.

You can file ST-1-X through MyTax Illinois if you originally filed that period through the same portal. The window for claiming a credit on an overpayment depends on timing: amendments filed between January 1 and June 30 can claim credit for overpayments during the current year and the prior 36 months; amendments filed between July 1 and December 31 have a 30-month lookback. There is no deadline for paying additional tax you owe, but interest and penalties keep running until you do.

Why Personal Liability Makes On-Time Filing Non-Negotiable

Illinois treats sales tax you collect from customers as money held in trust for the state. Under 35 ILCS 120/13, corporate officers, partnership members, LLC managers, and employees with a duty to file face felony charges for failure to file or for filing fraudulent returns:

  • Under $300 involved: Class 4 felony.
  • $300 or more: Class 3 felony.

The same Class 3 felony applies to anyone who accepts sales tax money as an agent for remittance and then fails to send it in. The criminal exposure sits on top of the civil tax, penalties, and interest the business already owes.

Remote Sellers Outside Illinois

If you sell into Illinois from out of state, you cross the economic nexus threshold at $100,000 or more in cumulative gross receipts from tangible personal property sold to Illinois buyers during the lookback period. As of January 1, 2026, the previous 200-transaction threshold is gone; the dollar threshold is the only trigger.13Illinois Department of Revenue. FY 2026-12, Destination-Based Retailers Occupation Tax Changes

Once you cross it, register with IDOR, collect Illinois sales tax on future sales, and file Form ST-1 on the frequency IDOR assigns. The filing process, deadlines, discount, and penalties all work the same way described above. If you sell through a marketplace like Amazon or eBay, the marketplace facilitator typically handles collection and remittance, but confirm with both the marketplace and IDOR whether your own independent sales push you over the threshold on their own.