2025 Illinois State Tax Deadlines
Illinois Individual income tax filing deadlines and extensions for 2025.
If you are a resident or have been involved in business operations within Illinois, you might be required to file Illinois State taxes. Illinois maintains a flat income tax rate of 4.95% for individuals, along with a unique dual corporate tax structure that combines income tax and replacement tax. This comprehensive guide outlines the key tax deadlines and considerations applicable to Illinois in 2025.
Illinois business tax deadlines for 2025
C Corporation deadlines and requirements
C Corporations in Illinois must file and pay Corporate Income Taxes by April 15, 2026.
Filing requirements include:
- Complete Form IL-1120 (Illinois Corporation Income and Replacement Tax Return)
- File online through MyTax Illinois or approved software
- File by mail must be postmarked by the due date
- Payment must be made by April 15, 2026
- Combined rate of 9.5% (7% income tax + 2.5% replacement tax)
Extension to file taxes in Illinois for 2025
The Extension Deadline for Illinois corporate income tax returns is November 16, 2026. Illinois automatically grants a seven-month extension on filing corporate income tax returns. This is an extension to FILE, not an extension to PAY—payment is still due April 15, 2026.
Pass-through entities
Illinois S Corporation and Partnership tax deadlines for 2025
S Corporations must file by March 16, 2026, while Partnerships must file by April 15, 2026.
Required forms include:
- Form IL-1120S – S Corporation Replacement Tax Return
- Form IL-1065 – Partnership Replacement Tax Return
Extension to file S Corporation and Partnership taxes in Illinois for 2025
The Extension Deadline for Illinois S Corporations returns is November 16, 2026, while Partnerships receive an extension until October 15, 2026. Illinois automatically grants these extensions without requiring separate applications. This is an extension to FILE, not an extension to PAY—payment is still due on the original deadlines.
Illinois individual tax considerations for 2025
Filing requirements and income thresholds
Illinois Individuals must file a State income tax return if they are required to file a federal return or if their Illinois base income exceeds specific thresholds.
The 2025 filing thresholds are:
- $13,850 for single taxpayers
- $27,700 for married filing jointly
- $20,800 for head of household filers
- $13,850 for married filing separately
Estimated tax deadline for Illinois 2025
Estimated tax payments are due:
- April 15, 2025
- June 15, 2025
- September 15, 2025
- January 15, 2026
Who must make estimated payments
You must make Illinois estimated income tax payments during 2025 if you expect to owe $1,000 or more in Illinois income tax after subtracting your withholding and credits. Individuals with business income, rental properties, or investment gains typically need to make quarterly payments.
Individual tax deadline for Illinois 2025
You must file and pay Individual Income Taxes in Illinois by April 15, 2026. Illinois accepts electronic filing through MyTax Illinois, significantly reducing processing time.
Available forms include:
- Form IL-1040 – Illinois Individual Income Tax Return
Extension to file taxes in Illinois for 2025
The Extension Deadline is October 15, 2026, to file your Illinois Individual Income tax return. Illinois automatically grants a six-month extension on filing personal income taxes without requiring separate State extension forms. This is an extension to FILE, not an extension to PAY—payment is still due April 15, 2026.
What Illinois tax professionals need to know
Several key considerations make the Illinois tax landscape unique for 2025:
Illinois's flat 4.95% individual income tax rate simplifies calculations, while the dual corporate tax structure (income tax plus replacement tax) creates additional complexity for businesses. The State offers limited tax credits compared to other states, with a primary focus on property tax relief programs.
Electronic filing requirements
Illinois encourages electronic filing for most taxpayers:
- C Corporations can file electronically through MyTax Illinois
- Partnerships and S Corporations benefit from faster processing through electronic systems
- Individuals can use MyTax Illinois for free electronic filing
How does Illinois determine residency
Illinois determines residency based on domicile and the amount of time spent in the State. Full-year residents pay tax on all income regardless of source, while part-year residents and nonresidents pay tax only on Illinois-source income.
Illinois's unique tax features for 2025
Dual corporate tax structure
C Corporations face Illinois's unique dual tax system, which includes a 7% corporate income tax and a 2.5% replacement tax, resulting in a combined rate of 9.5%.
Flat individual income tax
Illinois maintains a flat 4.95% income tax rate for Individuals, making it one of the few states with a single-rate individual income tax structure.
Property tax deduction
Illinois allows Individuals to deduct property taxes paid on their principal residence from Illinois' taxable income, providing significant tax relief in a high-property-tax state.
Sales tax changes
Beginning January 1, 2025, Illinois caps the retailers' discount on sales at $1,000 per month, affecting businesses that collect and remit sales tax.
Sources
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The material discussed on this page is meant for general illustration and/or informational purposes only and is not to be construed as investment, tax, or legal advice. You must exercise your own independent professional judgment, recognizing that advice should not be based on unreasonable factual or legal assumptions or unreasonably rely upon representations of the client or others. Further, any advice you provide in connection with tax return preparation must comply in full with the requirements of IRS Circular 230.
Please note that if any due date falls on a federal or state holiday or weekend, it may be adjusted to the next business day. Always verify current deadlines with the appropriate tax professional and authorities.
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