The Illinois ST-1 form is the sales and use tax return that retailers file with the Illinois Department of Revenue (IDOR) to report and remit Retailers’ Occupation Tax, Use Tax, and the E911 surcharge on prepaid wireless sales. If you sell tangible goods in Illinois, you file this return monthly, quarterly, or annually depending on how much tax you owe, and the deadline is the 20th of the month after the reporting period ends. IDOR expects most filers to submit the return electronically through MyTax Illinois.
Who Has to File
You file an ST-1 if you make retail sales of general merchandise, qualifying food, drugs, and medical appliances, or prepaid wireless telecommunications service in Illinois. That reaches beyond traditional storefronts. Service providers who transfer physical goods as part of their work also owe tax: a plumber who installs a water heater, for instance, owes tax on the cost of the heater under the Service Occupation Tax Act.1Illinois General Assembly. Illinois Code 35 ILCS 115 – Service Occupation Tax Act
Remote retailers selling into Illinois from out of state must register and file once their cumulative gross receipts from Illinois buyers reach $100,000 or more during any 12-month lookback period. A separate 200-transaction trigger used to apply, but Public Act 104-0006 eliminated it effective January 1, 2026. Only the dollar threshold matters going forward.2Illinois General Assembly. Public Act 104-0006
Marketplace facilitators such as Amazon or Etsy carry the same obligation. Once a facilitator meets the $100,000 threshold, it collects and remits the applicable state and local Retailers’ Occupation Tax on marketplace sales to Illinois customers, which relieves individual sellers of that duty for sales made through the platform.3Legal Information Institute. Illinois Admin Code tit 86 131.145 – Marketplace Facilitators
When you register with IDOR, you receive a Certificate of Registration that authorizes you to collect tax. IDOR issues these electronically through MyTax Illinois rather than mailing paper copies.4Illinois Department of Revenue. Can I Print a Copy of My Business Certificate of Registration or License From MyTax Illinois
How Often You File and When It Is Due
IDOR assigns your filing frequency based on your average monthly tax liability and reviews that figure as your business changes.5Illinois Department of Revenue. ST-1 Instructions
- Monthly if your average monthly liability is above $200.
- Quarterly if your average monthly liability is between $50 and $200.
- Annual if your average monthly liability is below $50.
The return and any tax owed are due by the 20th of the month following the reporting period. When the 20th lands on a weekend or holiday, the deadline shifts to the next business day. Seasonal businesses get no special schedule. IDOR averages liability across all 12 months, including zero-sales months, so a business open three months a year with $2,400 in total tax still averages $200 per month and files monthly.
What Goes on the Return
The ST-1 starts with your total gross receipts for the period, meaning everything you took in from sales, taxable or not. From that total you subtract deductions to reach taxable receipts. The most common deduction is sales for resale, which require a valid Certificate of Resale (Form CRT-61 or a buyer-created equivalent) on file. You must keep that certificate for at least three and a half years as proof the sale was exempt.6Illinois Department of Revenue. Certificate of Resale Other deductions apply to sales to exempt buyers such as government agencies and qualifying nonprofits.
You also have to keep complete transaction records supporting every figure on the return. IDOR requires you to hold these for three and a half years after you file the original or amended return. If IDOR has issued a notice of tax liability for a period, keep the records for that period until the matter is resolved.7Illinois Department of Revenue. Pub-113, Keeping Complete and Accurate Records
Destination-Based Tax Rates
Illinois sources sales to the destination, so you charge tax based on where the goods are delivered rather than where your store sits. The state rate is 6.25% on general merchandise and 1% on qualifying food, drugs, and medical appliances. Local governments add their own layers on top, so the combined rate at a Chicago delivery address can look very different from one in a rural county.8Illinois Department of Revenue. Use Tax Rates
If you file through MyTax Illinois, the system fills in the correct rates for your registered sites. Otherwise, IDOR’s Tax Rate Finder at mytax.illinois.gov lets you look up a specific location.5Illinois Department of Revenue. ST-1 Instructions Getting location data wrong carries a real cost. Beginning January 1, 2026, if you fail to provide enough information for IDOR to determine the correct delivery location, the department will assess tax on those sales at a flat 15% rate.9Illinois Department of Revenue. Destination-Based Sales Tax Assistance
Reporting Multiple Locations
If you sell from more than one location, attach Form ST-2 (Multiple Site Form) to your ST-1 to break the tax down by site. The combined ST-2 totals must match the corresponding lines on the ST-1.10Illinois Department of Revenue. ST-2 Instructions
For remote retailers and marketplace facilitators, “site” means the Illinois destination where the item is delivered. You register a changing location for each local jurisdiction where you have made a sale and report aggregate taxable receipts for all deliveries into that jurisdiction under a single entry. MyTax Illinois now displays all changing locations on one screen during electronic filing, so you no longer have to add or remove them before each return.9Illinois Department of Revenue. Destination-Based Sales Tax Assistance
You cannot report negative receipts on the ST-2 for any location. If a customer refund for a prior period would push a location’s receipts below zero, file an amended return for the period the original sale occurred instead of netting it against the current one.
Prepaid Wireless: E911 and ITAC
If you sell prepaid wireless telecommunications service, the ST-1 has a separate schedule (Schedule B) for the E911 surcharge and the ITAC (Illinois Telecommunications Access Corporation) assessment. These sit on their own lines and are not part of the standard sales tax calculation.11Illinois Department of Revenue. ST-1 – Sales and Use Tax and E911 Surcharge Return
The E911 surcharge has one rate for Chicago locations and another for the rest of the state. The ITAC assessment is a separate rate set by the Illinois Commerce Commission and changes each year on July 1. Check the Tax Rate Database at tax.illinois.gov before each filing period rather than reusing last period’s figures.
Filing and Paying Through MyTax Illinois
Most businesses file the ST-1 electronically through MyTax Illinois. The portal walks you through each line, auto-populates tax rates for your registered sites, and issues a confirmation number when you submit. That number is your proof of timely filing, so save it.12Illinois Department of Revenue. Sales and Use Tax Forms
You can pay by ACH debit during the electronic filing process, or by mailing a check with a payment voucher in the limited cases where paper filing is still allowed. File and pay on time and you earn a collection allowance of 1.75% of the tax due. The form calculates the discount for you during electronic filing. Missing the deadline by a single day forfeits it entirely.
Late Filing Penalties
Miss the deadline and the Uniform Penalty and Interest Act kicks in with a two-tier structure. The first tier is automatic: 2% of the tax due, capped at $250. If you still have not filed within 30 days after IDOR mails a nonfiling notice, a second penalty applies, equal to the greater of $250 or 2% of the tax shown on the return, up to a $5,000 cap. Interest runs on top of both.13Legal Information Institute. Illinois Admin Code tit 86 700.300 – Penalty for Late Filing or Failure to File
Criminal exposure is a separate matter and far harsher. Under the Retailers’ Occupation Tax Act, filing a fraudulent return or failing to file at all is a Class 4 felony when the amount due is under $300, and a Class 3 felony (carrying two to five years of potential incarceration) when the amount is $300 or more. That reaches business owners, officers, and accountants who knowingly enter false information.14Illinois General Assembly. 35 ILCS 120/13
Fixing a Return or Claiming an Overpayment
Find an error after filing? Use Form ST-1-X (Amended Sales and Use Tax and E911 Surcharge Return) to correct it. IDOR encourages filing the amendment through MyTax Illinois, though a paper version is available.15Illinois Department of Revenue. ST-1-X Amended Sales and Use Tax and E911 Surcharge Return
If you overpaid tax on a prior return, Form ST-6 lets you claim the overpayment as a credit memorandum, transfer it to another Illinois tax account, or request a cash refund. The lookback window shifts during the year: claims filed between January 1 and June 30 reach back 36 months, while claims filed starting July 1 reach back 30 months. The form must be signed by the business owner, an officer, or whoever is authorized to sign the original return.16Illinois Department of Revenue. ST-6 Claim for Sales and Use Tax Overpayment / Request for Action on a Credit Memorandum