Illinois sales tax returns are filed online through MyTax Illinois, the Illinois Department of Revenue's free account portal, using Form ST-1. The return and any payment are due on the 20th of the month after your reporting period ends (the next business day if the 20th is a weekend or holiday). This guide covers who files and how often, how to file step by step, what to do about local tax and zero returns, and what late filing costs.
This article is educational information, not tax advice. Filing rules, thresholds, and penalties can change, so confirm current requirements with the Illinois Department of Revenue before you file.
Illinois sales tax filing at a glance
- Who administers it: Illinois Department of Revenue.
- Online portal: MyTax Illinois at mytax.illinois.gov.
- Return: Form ST-1, Sales and Use Tax and E911 Surcharge Return. Form ST-2 attaches to it to break out tax by location.
- Filing frequency: Monthly, quarterly, or annual, based on your average monthly tax liability.
- Due date: The 20th of the month after the reporting period. Annual returns are due January 20.
- Zero returns: Required for every reporting period, even with no sales.
- Payment: Electronically through MyTax Illinois or by ACH credit. Some taxpayers are required to pay electronically.
- Economic nexus: $100,000 in gross receipts or 200 separate transactions for remote retailers.
Who has to file, and how often
Every retailer registered with the Department of Revenue has to file an ST-1 for each reporting period. That includes remote retailers that meet Illinois's economic nexus threshold: $100,000 or more in cumulative gross receipts from sales, or 200 or more separate transactions, in a 12-month period. The Department checks this quarterly, as of March 31, June 30, September 30, and December 31. Our Illinois sales tax guide covers registration and nexus in more detail. Selling software? Our post on whether SaaS is taxable in Illinois explains how it is treated there.
The Department sets your filing frequency from your average monthly tax liability and notifies you if it changes:
| Frequency | When it applies | Due date |
|---|---|---|
| Monthly | Average monthly liability greater than $200 | 20th of the following month |
| Quarterly | Average monthly liability of $50 to $200 | 20th of the month after the quarter ends |
| Annual | Average monthly liability less than $50 | January 20 of the following year |
Taxpayers whose average tax due on the ST-1 is at least $20,000 a month must make four payments each month, on the 7th, 15th, 22nd, and last day of the month, and must make them electronically. Our Illinois sales tax due dates page lists upcoming dates for every state.
Before you start: set up MyTax Illinois
MyTax Illinois is free. The Department says it fills in the tax rates for each of your registered locations and lets you add or remove locations, calculate tax for multiple sites, and pay electronically. To get ready:
- Register your business. Illinois businesses register with Form REG-1, and our sales tax permit overview explains what registration involves. The Department sends your filing frequency after registration.
- Log in to MyTax Illinois and confirm your registered locations.
- Have your records ready for the period: gross receipts, deductions, and sales by location or by destination.
Step-by-step: filing an Illinois sales tax return in MyTax Illinois
- Log in to MyTax Illinois and open your sales and use tax account.
- Select the ST-1 for the reporting period you are filing.
- Enter your receipts and deductions on the ST-1 lines. For sales to resellers, see our Illinois resale certificate guide.
- Complete the ST-2 for each location. MyTax Illinois shows all of your sales locations on one screen. The ST-2 page totals for each line must equal the matching line on the ST-1.
- Review the tax due, including any timely-filing discount.
- Pay. Choose an electronic payment in MyTax Illinois, or use ACH credit through your bank.
- Save your confirmation with your records for the period.
Filing in Illinois plus other states? Kintsugi files and remits for you, from $75 per filing, with free monitoring and no per-state subscription. Start free or book a demo.
Local tax, ST-2, and destination sales
Illinois local tax is reported by location, and Form ST-2 is where you do it. The Department requires an ST-2 when you sell at more than one location. Remote retailers and marketplace facilitators must also use it, and for them a "site" is the destination in Illinois where the item is delivered. They report the total taxable receipts for all sales to a site, combining everything sold into one municipality or business district under a single entry.
If you sell into many Illinois cities, that means one entry per local government where you made a sales. MyTax Illinois lets you add these sites through its Maintain Locations link. Check rates for a specific address with the Illinois sales tax calculator.
Filing a zero return
You must file even when you had no receipts. The Department states that you must file a processable, signed ST-1 for each reporting period regardless of whether there are receipts or purchases to report, and that if you have no receipts you must file a "zero" return.
Amending an Illinois return
To correct an ST-1 you already filed, use Form ST-1-X. You need it to pay more tax, claim a credit for an overpayment, respond to a notice or bill, correct line items with no change in tax, or amend an ST-2. File one ST-1-X per reporting period; you cannot combine several months or quarters on one form. You can file it in MyTax Illinois if your original return was filed electronically.
The window for claiming credits depends on when you file: between January 1 and June 30 you can claim credits for the current year plus the prior 36 months, and between July 1 and December 31, the current year plus the prior 30 months.
Payment methods and electronic payment rules
Businesses can pay through MyTax Illinois or by ACH credit, and the Department also lists credit card payment for business taxes. Taxpayers required to pay electronically must use ACH debit or ACH credit.
- Electronic payment is required when your annual liability for Retailers' Occupation and Use Tax is $20,000 or more.
Discount for filing on time
Illinois lets retailers keep a small share of the tax they collect if they file and pay on time. Starting January 1, 2025, the discount is 1.75% of the tax due, or $5 per year if that is greater, capped at $1,000 per month. You lose it if the return or payment is late.
Penalties and interest for late filing
- Late filing: The lesser of $250 or 2% of the tax required to be shown due, after payments and credits.
- Late payment, 1 to 30 days: 2% of the tax.
- Late payment, 31 or more days: 10% of the tax.
- Paid after an audit or investigation begins: 15% of the unpaid amount.
- Interest: Illinois reviews interest rates twice a year, on January 1 and July 1. See the Department's Publication 103 for the current rate.
Common mistakes to avoid
- Skipping zero returns. Every reporting period needs a return, even with no receipts.
- Combining periods on an amended return. Each ST-1-X covers one period.
- Mismatched ST-1 and ST-2 totals. The ST-2 page totals must equal the ST-1 lines.
- Missing destination sites. Remote retailers report by delivery destination, not by where the business is located.
- Paying at the deadline. Filers with $20,000 or more in average monthly tax pay four times a month.
- Losing the discount. A late return or payment gives up the 1.75% discount and adds a penalty.
More state filing guides
Filing in more than one state? These step-by-step guides cover the portals, due dates, and penalties in other states. See them all in our state-by-state guide to filing sales tax online.
- How to file Ohio sales tax online
- How to file Pennsylvania sales tax online
- How to file Washington sales tax online
Let Kintsugi file for you
If you file in more than one state, or you would rather not log in to MyTax Illinois every month, Kintsugi's sales tax filing software prepares and files Illinois returns on your assigned schedule, including zero returns, and remits payment. You review the numbers; Kintsugi handles the portal. Kintsugi's free plan also monitors your sales across every US state so you know where you cross economic nexus. Filing starts at $75 per filing, with no per-state subscription. See pricing.
Illinois sales tax filing FAQs
Can I file Illinois sales tax online for free?
Yes. MyTax Illinois is a free online account management program from the Department of Revenue.
What form do I use to file Illinois sales tax?
Form ST-1, the Sales and Use Tax and E911 Surcharge Return. Form ST-2 attaches to it to show tax by location, and Form ST-1-X amends a return you already filed.
When is Illinois sales tax due?
On the 20th of the month after the reporting period. Annual returns are due January 20. If the due date falls on a weekend or holiday, it moves to the next business day.
Do I have to file if I had no sales?
Yes. File a zero return for every reporting period.
How do I know if I file monthly, quarterly, or annually?
It depends on your average monthly liability: more than $200 is monthly, $50 to $200 is quarterly, and less than $50 is annual. The Department notifies you of any change.
What if I miss the deadline?
File and pay as soon as possible. The late-filing penalty is the lesser of $250 or 2% of the tax due, and late payment is 2% for 1 to 30 days and 10% for 31 or more days.
Sources
Checked September 29, 2026.
- Illinois Department of Revenue, Sales and Use Taxes
- Illinois Department of Revenue, ST-1 Instructions for reporting periods January 2026 and after
- Illinois Department of Revenue, ST-2 Instructions
- Illinois Department of Revenue, ST-1-X Instructions
- Illinois Department of Revenue, Requirements for Retailers who File Form ST-1
- Illinois Department of Revenue, Who Must Make Electronic Payments?
- Illinois Department of Revenue, Pub-103, Penalties and Interest for Illinois Taxes
