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Illinois Individual Income Tax Filing deadlines and extensions for 2025 for tax professionals.
If you have clients who are residents or have been involved in significant business operations within Illinois, then they might be required to file Illinois State Taxes. This overview examines the most crucial tax deadlines and tax extensions for Illinois in 2025.
If your clients are residents or have been involved in significant business operations within Illinois, then they might be required to file Illinois State Taxes. This page outlines important tax deadlines and tax extensions for Illinois in 2025.
Illinois C Corporation Tax Deadlines for 2025
You must file and pay Corporate Income Taxes in Illinois by April 15, 2026.
Extension to File Taxes in Illinois for 2025
The Extension Deadline for Illinois corporate tax returns is November 16, 2026.
This is an extension to FILE, not an extension to PAY – payment is still due April 15, 2026.
Illinois S Corporation & Partnership Tax Deadlines for 2025
Partnership – You must file and pay in Illinois by April 15, 2026.
S Corporation – You must file and pay in Illinois by March 16, 2026.
Extension to File S Corporation & Partnership Taxes in Illinois for 2025
Partnership – The Extension Deadline for Illinois partnership tax returns is October 15, 2026.
S Corporation – The Extension Deadline for Illinois small business corporate tax returns is November 16, 2026.
Illinois automatically grants a six-month extension for filing partnership tax returns and a seven-month extension for small business corporate tax returns. This means you do not need to file for an extension in Illinois.
This is an extension to FILE, not an extension to PAY – payment is still due March 15, 2026.
Estimated Tax Deadline for Illinois 2025
Estimated tax payments can be made in four equal installments based on either 90% of the expected liability for the year 2025 or 100% of the liability for the year 2024 to avoid penalties, provided payments are made timely.
Individual Tax Deadline for Illinois 2025 You must file and pay Individual Income Taxes in Illinois by April 15, 2026.
Extension to File Taxes in Illinois for 2025
Illinois automatically grants a six-month extension on filing personal income taxes. This means you do not need to file for an extension in Illinois.
This is an extension to FILE, not an extension to PAY – payment is still due April 15, 2026.
For estates and trusts, Illinois has specific filing requirements and deadlines that may differ. It’s recommended to consult the Illinois Department of Revenue for the most current information and guidelines.
Farmers and fishermen with at least two-thirds of their gross income derived from farming or fishing have specific guidelines for estimated tax payments and filing deadlines. Detailed advice should be sought from a tax professional or the Illinois Department of Revenue to ensure compliance with these specialized rules.
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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.
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