To file sales tax in Illinois, you submit Form ST-1, the Sales and Use Tax and E911 Surcharge Return, through the MyTax Illinois portal at mytax.illinois.gov by the 20th of the month after your reporting period ends. The form captures your gross receipts, deductions, tax owed by category, and any use tax on items you bought without paying Illinois tax. Payment goes through the same portal when you submit.
Register Your Business First
You cannot file Form ST-1 until the Illinois Department of Revenue has issued you a Certificate of Registration. You apply using Form REG-1, the Illinois Business Registration Application, either on paper or through MyTax Illinois (faster). The application asks for your FEIN or Social Security Number, legal business name, a description of your activities, and the names and addresses of owners or officers.1Illinois Department of Revenue. REG-1 Illinois Business Registration Application
Once approved, you receive a Certificate of Registration and an eight-digit Illinois Account ID (XXXX-XXXX). You then create your MyTax Illinois login, which you use for every return and payment going forward.2Illinois Department of Revenue. PIO-117 How to Register Your Illinois Business
Retailer Certificates of Registration expire after one year and renew automatically as long as you stay current on filings and payments. Falling behind stops the automatic renewal.3Illinois Department of Revenue. Taxpayer Answer Center – Certificate of Registration Renewal
When Your Return Is Due
The department assigns your filing frequency based on your average monthly tax liability:
- Monthly if your average monthly liability is more than $200
- Quarterly if it is between $50 and $200
- Annually if it is less than $50
The department reviews these levels periodically and notifies you when your frequency changes.4Illinois Department of Revenue. Form ST-1 Instructions for Reporting Periods January 2026 and After
Whatever your frequency, the deadline is the 20th of the month after the reporting period ends. A monthly filer’s January return is due February 20th. A quarterly filer covering January through March files by April 20th. An annual filer covering a calendar year files by January 20th. When the 20th falls on a weekend or holiday, the deadline moves to the next business day.
Very large retailers face an additional step. If your average monthly liability exceeds the statutory threshold, the department will notify you that you must make quarter-monthly (accelerated) payments, remitting tax multiple times per month rather than once.5Illinois Department of Revenue. IDR-825 Guidelines for Quarter-Monthly (Accelerated) Payments
Gather Your Records Before You Log In
Pull your sales ledger or point-of-sale reports for the reporting period before opening MyTax Illinois. You need the total dollar amount of everything your business collected: every cash, check, and credit card transaction, including the tax you collected from customers. You also need your eight-digit Illinois Account ID and your MyTax login.2Illinois Department of Revenue. PIO-117 How to Register Your Illinois Business
If you claimed any exempt sales, pull the supporting paperwork. For resale transactions, you should have a Certificate of Resale (Form CRT-61) or equivalent statement from each purchaser, signed and listing their Illinois retailer or reseller account ID. Sellers must keep these certificates for at least three and a half years.6Illinois Department of Revenue. CRT-61 Certificate of Resale Instructions Sales to exempt organizations like schools or government agencies require the buyer’s valid tax-exempt identification number.
If you bought merchandise or equipment for your own business use without paying Illinois tax, keep those purchase records too. Use tax on those items gets reported on the same Form ST-1.
If you sell from more than one location in Illinois, you collect tax at each location’s rate and report the breakdown by attaching Form ST-2, the Multiple Site Form.7Illinois Department of Revenue. ST-2 Instructions for Reporting Periods January 2026 and After Rate lookup tools on the department’s website give you the exact combined rate for each location, and checking them before every filing takes about two minutes.
Walking Through Form ST-1
The electronic version on MyTax Illinois auto-calculates most totals, but knowing what each section asks for prevents data-entry mistakes that generate notices weeks later.
Gross Receipts and Deductions
Line 1 is your gross receipts: the total of all sales, leases, and rentals during the period, including any tax you collected and any service charges. This should match your internal books exactly.4Illinois Department of Revenue. Form ST-1 Instructions for Reporting Periods January 2026 and After
Line 2 is deductions, which flow from Schedule A on the back of the form. Schedule A categories include taxes collected, resale purchases, interstate commerce sales, sales to exempt organizations, uncollectible debts, enterprise zone sales, and others.8ILLINOIS DEPARTMENT OF REVENUE. ST-1 Sales and Use Tax and E911 Surcharge Return The Line 2 total can never exceed Line 1. Line 3 is the difference, your taxable net receipts.4Illinois Department of Revenue. Form ST-1 Instructions for Reporting Periods January 2026 and After
Every deduction has to be backed by documentation. The department can request proof during an audit, and unsupported deductions get added back to your taxable base with penalties on top.
Tax by Category
After reaching your taxable net receipts on Line 3, you split that amount by category. General merchandise is taxed at the base state rate of 6.25%.9Justia. Illinois Code 35 ILCS 120 Retailers Occupation Tax Act Qualifying food for off-premises consumption, prescription drugs, and medical appliances are taxed at a reduced state rate of 1%. Lines 4 through 8 handle the splits, and the entries across all categories must add up to Line 3.4Illinois Department of Revenue. Form ST-1 Instructions for Reporting Periods January 2026 and After Local taxes for your jurisdiction get applied within Schedule A based on your business location.
Use Tax on Your Own Purchases
Step 5 of Form ST-1 covers use tax: the tax you owe on items you bought for business use without paying Illinois sales tax. This typically happens when you order supplies or equipment from an out-of-state vendor who does not collect Illinois tax, or when you pull inventory off your shelves for your own use instead of selling it. You enter the cost of those items on Lines 12 through 14, broken out by general merchandise, drugs and medical appliances, and items taxed at other rates, and the form calculates the tax.4Illinois Department of Revenue. Form ST-1 Instructions for Reporting Periods January 2026 and After
The Vendor Discount for Filing on Time
Illinois rewards on-time filers. If your return and payment arrive by the due date, you can claim a discount equal to 1.75% of the tax owed, with a minimum of $5 per calendar year. For returns due on or after January 1, 2025, the discount is capped at $1,000 per month.4Illinois Department of Revenue. Form ST-1 Instructions for Reporting Periods January 2026 and After
For most small and mid-size retailers, 1.75% of monthly tax is well under the $1,000 ceiling, so you get the full percentage. The cap matters mainly for high-volume businesses whose 1.75% calculation would otherwise exceed it. The discount is calculated on Step 4, Line 10. A separate $1,000 monthly cap applies to the E911 Surcharge discount on Schedule B, and the ITAC Assessment discount is calculated separately with no cap.
Submit and Pay
Review the populated return before submitting. The system requires an electronic signature attesting that the information is true and correct to the best of your knowledge.8ILLINOIS DEPARTMENT OF REVENUE. ST-1 Sales and Use Tax and E911 Surcharge Return Once you submit, the portal prompts you to pay. Options:
- ACH debit, where you authorize the department to pull funds from your bank account. This is the most common method and is built into the portal.
- ACH credit, where you instruct your own bank to push funds to the department. This requires requesting banking instructions through MyTax Illinois, which takes about seven to ten business days the first time.10Illinois Department of Revenue. ACH Credit Payment Information
- Credit card, processed by a third-party vendor that charges a convenience fee as a percentage of your payment.
After payment clears, the system generates a confirmation number. Download or print the transaction summary; that confirmation is your proof of filing if a question comes up later.
Fixing a Return You Already Filed
If you catch an error after filing, you correct it with Form ST-1-X, the Amended Sales and Use Tax and E911 Surcharge Return. You need one ST-1-X for each period you want to fix. You can file it electronically through MyTax Illinois if the original was filed there.11Illinois Department of Revenue. ST-1-X Instructions for Amended Sales and Use Tax Return
If the original included Form ST-2 for multiple locations, you must also file Form ST-2-X completed in its entirety. Amended deductions require Schedule A-X, and amended E911 Surcharge figures need Schedule B-X. Missing any supplementary form will delay processing or get the amendment rejected.
What Late Filing or Payment Costs
Penalties stack. You can owe both a filing penalty and a payment penalty on the same return.
Late Filing
Filing late triggers a first penalty equal to the lesser of $250 or 2% of the tax due, reduced by any timely payments. If you still have not filed within 30 days after the department sends a notice of nonfiling, a second penalty applies: the greater of $250 or 2% of the tax shown due, up to $5,000.12Illinois Department of Revenue. Pub-103 Penalties and Interest for Illinois Taxes
Late Payment
Paying late carries its own penalty, scaled to how late:
- 1 to 30 days late: 2% of the unpaid tax
- 31 or more days late: 10% of the unpaid tax
- Paid after an audit begins: 15% of the unpaid amount
- Paid more than 30 days after an audit-prepared amended return: 20% of the unpaid amount
The jump from 2% to 10% happens at exactly 31 days, which catches retailers who assume they have a few extra weeks to find the money.12Illinois Department of Revenue. Pub-103 Penalties and Interest for Illinois Taxes
Interest
Unpaid tax accrues interest at the federal underpayment rate, which the department reviews every January 1 and July 1. Through June 30, 2026, the rate is 7%.13Illinois Department of Revenue. Interest Rates Interest runs from the original due date until the tax is paid in full.
How Long to Keep the Records
Illinois requires you to keep all records supporting the figures on Form ST-1 and Form ST-2 for at least three and a half years after filing the original or amended return. That includes sales receipts, point-of-sale reports, Certificates of Resale, exempt-sale documentation, and purchase records for use tax items.14Illinois Department of Revenue. Retailers Overview Keeping Complete and Accurate Records
If the department has issued a Notice of Tax Liability or Final Notice of Tax Due, keep the records for that period until the liability is resolved or discharged, even if that runs longer than three and a half years. Storing your MyTax confirmation receipts alongside your sales records keeps everything an auditor might ask for in one place.