Illinois Sales Tax Forms, Deadlines, and Filing Instructions (For Businesses)

Overview

Businesses registered for Illinois sales and use tax must file periodic returns, report taxable sales, and remit the tax collected. Filing requirements depend on the business’s assigned filing frequency and reporting structure.

This guide covers the main Illinois sales tax forms, filing deadlines, and filing instructions for businesses.

Illinois Sales Tax Forms

The primary return used by businesses is the Illinois Sales and Use Tax and E911 Surcharge Return (Form ST-1).

Businesses with multiple selling locations may also need to complete Form ST-2, Multiple Site Form, which is used to report sales and tax by location. Illinois also provides an amended return, Form ST-1-X, for correcting previously filed returns.

For official forms and schedules, see the Illinois sales and use tax forms page.

Product-Specific Reporting Requirements

Illinois requires businesses to report certain categories of sales separately on sales tax returns. This is particularly relevant for sellers of groceries, medicines, and other items subject to reduced rates or special treatment.

Failure to correctly classify and report these transactions may result in underpayment of tax or filing discrepancies during audit.

Reporting Food Sales (Post-2026 Changes)

Effective January 1, 2026, Illinois eliminated the 1% state sales tax on grocery items. However, grocery sales must still be reported separately on Form ST-1.

Retailers are required to:

• Report qualifying grocery sales in the designated “food” category
• Exclude these amounts from general merchandise subject to the 6.25% rate
• Apply any applicable local grocery taxes where imposed

For official guidance, see FY 2026-03 Grocery Tax Changes.

Reporting Drugs and Medical Appliances

Sales of qualifying drugs and medical appliances must be reported separately from general merchandise. These items are subject to a reduced 1% state rate, but must still be included in total taxable receipts reported on the return.

Retailers should:

• Track qualifying items separately in their accounting system
• Apply the correct tax rate at the transaction level
• Report reduced-rate sales in the appropriate section of Form ST-1

See IDOR guidance on drugs and medical appliances for classification rules.

Mixed Sales and Line Item Reporting

Businesses selling both general merchandise and reduced-rate items must ensure that sales are properly categorized at the line-item level. Illinois does not allow simplified reporting based on blended rates.

Common issues include:

• Incorrect grouping of grocery and prepared food sales
• Failure to distinguish prescription vs. non-prescription items
• Applying a single tax rate to all items on an invoice

Impact on Form ST-1 Filing

Form ST-1 requires reporting of gross receipts, deductions, and taxable sales by category. Businesses must ensure that:

• Reduced-rate sales are properly deducted from general merchandise totals
• Taxable base reflects correct classification of products
• Local tax components are applied based on sourcing rules

For filing instructions and access to the online filing system, refer to the Illinois Department of Revenue Sales and Use Tax page.

Recordkeeping Requirements

Illinois expects businesses to maintain detailed records supporting reported sales tax amounts. This includes:

• Item-level sales data
• Tax rate applied per transaction
• Exemption certificates (if applicable)

Inadequate documentation is a common issue during audits, particularly for businesses applying reduced rates to food or medical products.

Filing Frequency

Illinois filing frequency depends on the taxpayer’s assigned reporting status.

• Monthly filing – generally for businesses with higher tax liability
• Quarterly filing – for certain businesses assigned quarterly reporting
• Annual filing – for certain smaller businesses assigned annual reporting

The Illinois Department of Revenue assigns the required filing frequency and businesses must file according to that schedule.

Filing Deadlines

Illinois sales tax returns are generally due on the 20th day of the month following the reporting period.

• Monthly filers: due on the 20th day of the following month
• Quarterly filers: due on the 20th day of the month following the quarter
• Annual filers: due on January 20 of the following year

If the due date falls on a weekend or holiday, the return and payment are generally due the next business day.

For official due-date guidance, see the Illinois sales and use tax information page.

What Must Be Reported

• Total gross sales
• Taxable sales
• Exempt sales and deductions
• State and local sales tax collected
• Use tax due on taxable purchases
• E911 surcharge and other applicable items included on the return

Businesses with more than one location may need to allocate sales by location using Form ST-2.

How to File

Illinois strongly encourages electronic filing, and many businesses are required to file electronically. Businesses can file and manage their returns through MyTax Illinois.

Illinois also provides detailed filing instructions in the ST-1 Instructions.

Payment of Tax

Payments are generally made electronically when filing through MyTax Illinois.

Businesses that file electronically and pay on time may qualify for the retailers’ discount described in the Illinois instructions.

Common Compliance Issues

• Missing the filing deadline
• Failing to file Form ST-2 when multiple locations are involved
• Using the wrong reporting period or filing frequency
• Incorrectly reporting destination-based or location-based sales
• Failing to amend returns properly when corrections are needed

Amended Returns

If a business needs to correct a previously filed sales tax return, it should use Form ST-1-X. Illinois provides separate amended-return instructions for businesses filing corrected periods.

Additional Resources

• Illinois destination-based sales tax assistance
• Sales tax calculator

Final Notes

Illinois sales tax compliance requires businesses to use the correct return, follow the assigned filing frequency, and properly report sales by location where required. Businesses should regularly review Illinois Department of Revenue guidance to ensure accurate reporting and timely filing.