Illinois Business Tax Deadlines (2026)
Next: June 15, 2026 — Federal & Illinois Q2 Estimated Tax Payment
Next Deadline: June 15, 2026 — Federal & Illinois Q2 Estimated Tax Payment
Federal Tax Deadlines (2026)
| Form | Who Files | Due Date | Extension Deadline |
|---|---|---|---|
| Form 1040 (Schedule C) | Sole proprietors | April 15 | October 15 |
| Form 1065 | Partnerships, Multi-member LLCs | March 15 | September 15 |
| Form 1120-S | S-Corporations | March 15 | September 15 |
| Form 1120 | C-Corporations | April 15 | October 15 |
| Form 990 | Nonprofits | May 15 | November 15 |
| Estimated Taxes (Q1) | All | April 15 | — |
| Estimated Taxes (Q2) | All | June 15 | — |
| Estimated Taxes (Q3) | All | September 15 | — |
| Estimated Taxes (Q4) | All | January 15, 2027 | — |
Illinois State Tax Deadlines (2026)
| Tax Type | Due Date | Form/Filing | Notes |
|---|---|---|---|
| Individual Income Tax | April 15 | Form IL-1040 | Flat 4.95% rate |
| Corporate Income Tax | April 15 | Form IL-1120 | 7% rate + 2.5% PPRT = 9.5% |
| S-Corp Return | March 15 | Form IL-1120-ST | 1.5% replacement tax |
| Partnership Return | March 15 | Form IL-1065 | 1.5% replacement tax |
| Sales Tax (Monthly) | 20th of following month | ST-1 via MyTax Illinois | State rate 6.25% |
| Withholding Tax (Monthly/Semi-weekly) | Varies by payroll | IL-501 | Employers |
| Annual Report | Anniversary of first day of anniversary month | Filed with Secretary of State | $75 (LLC); $75 (Corp) |
| Estimated Income Tax (Q1) | April 15 | Form IL-1040-ES / IL-1120-ES | — |
| Estimated Income Tax (Q2) | June 15 | Form IL-1040-ES / IL-1120-ES | — |
| Estimated Income Tax (Q3) | September 15 | Form IL-1040-ES / IL-1120-ES | — |
| Estimated Income Tax (Q4) | January 15, 2027 | Form IL-1040-ES / IL-1120-ES | — |
Quarterly Estimated Tax Deadlines in Illinois
Illinois follows the federal estimated tax payment schedule:
Estimated payments are required if you expect to owe $1,000 or more (individual) or $400 or more (corporate) in Illinois income tax.
Illinois-Specific Tax Requirements
Illinois has a flat individual income tax rate of 4.95%. For corporations, the total effective rate is 9.5% — a 7% corporate income tax plus a 2.5% Personal Property Replacement Tax (PPRT). S-corporations and partnerships also owe the PPRT at 1.5% of net income, making Illinois one of the few states that taxes pass-through entities at the entity level. This replacement tax is unique to Illinois and was originally enacted to replace local personal property taxes.
Illinois's state sales tax rate is 6.25%, with local taxes pushing combined rates above 10% in some areas (Chicago's combined rate is approximately 10.25%). Groceries and drugs are taxed at a reduced rate of 1%. The economic nexus threshold for remote sellers is $100,000 in sales or 200 transactions. Businesses register and file through the MyTax Illinois portal.
Illinois requires annual reports filed with the Secretary of State ($75 for both LLCs and corporations). Employers must register for withholding and file at frequencies determined by payroll size. Illinois does not have a franchise tax or gross receipts tax beyond the PPRT. The state offers an elective Pass-Through Entity Tax for S-corps and partnerships.
What Happens If You Miss an Illinois Tax Deadline?
Illinois Department of Revenue
Get Your Books Ready Before Tax Season
Illinois's replacement tax on pass-throughs catches business owners off guard. And with combined sales tax rates over 10% in Chicago, there's a lot riding on accurate books.
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