If you conducted business or earned income in Illinois, you may be subject to Illinois state taxes. If this applies to you, please find below the details regarding the R&D tax credit application, key tax deadlines, and extension information for 2024.
In Illinois, you may:
File your taxes online for free via My Tax Illinois
When filing by mail, ensure that your documents are postmarked by the due date.
Federal filing is not required.
Amendments are allowed up to 3-years from the original date of filing.
Overview, Eligibility, and Limitations
Overview, Eligibility, and Limitations
Research and Development Tax Credit Program
For tax years ending before January 1, 2022, a non-refundable credit is allowed against the regular income tax for increasing research activities in Illinois in an amount equal to 6.5% of qualifying expenditures.
Eligible Entities
C-Corporations, S-Corporations, LLCs, Partnerships
Credit Carryforward
If the available credit exceeds the current year tax liability, the unused credit can be carried forward for 5 years or until exhausted, whichever occurs first. Apply the carryover to the earliest taxable year.
Credits cannot be carried back to prior tax years.
The research credit is not refundable.
Credit Limitations
You may take this credit if you have certain qualifying expenses for increasing qualified research activities in Illinois.
You may not take this credit for the following types of activities:
Research conducted after the beginning of commercial production
Research adapting an existing product or process to a particular customer’s need
Duplication of an existing product or process
Surveys or studies
Research relating to certain internal-use computer software
Research conducted outside Illinois
Research in the social sciences, arts, or humanities
Research funded by another person (or government entity)
The tax credit will be repealed from statute on December 31, 2031
Illinois Public Act 10-0595 - Credit Code 53401
Partnership
You must file in Illinois by April 15, 2025.
Applicable R&D Forms
Form IL-1299-D – Research Income Tax Credits (for corporations and fiduciaries)
File the above form with the following tax forms:
Form IL-1065 – Partnership Replacement Tax Return
Extension to File Taxes in Illinois for 2024
Taxes owed in Illinois for the tax year 2024 must be paid by April 15, 2025.
No separate extension filing is required in Illinois.
Illinois automatically grants a 6-month extension for Partnership tax returns.
Partnership: the extension deadline is September 15, 2025.
Note that this extension pertains to the filing deadline, not the payment deadline.
Payment of taxes owed is still due by April 15, 2025.
S-Corporation
You must file in Illinois by March 15, 2025.
Applicable R&D Forms
Form IL-1299-D – Research Income Tax Credits (for corporations and fiduciaries)
File the above form with the following tax forms:
Form IL-1120S-ST – Small Business Corporation Replacement Tax Return
Extension to File Taxes in Illinois for 2024
Taxes owed in Illinois for the tax year 2024 must be paid by March 15, 2025.
No separate extension filing is required in Illinois.
Illinois automatically grants a 7-month extension for S-Corporation tax returns.
S-Corporation: the extension deadline is October 15, 2025.
Note that this extension pertains to the filing deadline, not the payment deadline.
Payment of taxes owed is still due by March 15, 2025.
C-Corporation
The due date is based on the end date of the corporation's tax year.
If your tax year ends on:
Standard Calendar Year, December 31,
due on April 15, 2025.
Fiscal Year date other than June 30,
due on or before the 15th day of the 4th month after the close of the tax year.
Fiscal year date on June 30,
due on or before the 15th day of the 3rd month after the close of the tax year.
Applicable R&D Forms
Form IL-1299-D – Research Income Tax Credits (for corporations and fiduciaries)
File the above form with the following tax forms:
Form IL-1120 – Illinois Corporation Franchise or Income Tax Return
Extension to File Taxes in Illinois for 2024
Taxes owed in Illinois must be paid by the appropriate due date above.
No separate extension filing is required in Illinois.
Illinois automatically grants an extension for C-Corporation tax returns.
Standard Calendar Year, December 21, grants an extension of 7 months.
The extension deadline is October 15, 2025.
Fiscal Year date other than June 30, grants an extension of 7 months.
Fiscal year date on June 30, grants an extension of 8 months.
Note that this extension pertains to the filing deadline, not the payment deadline.
Payment of taxes owed is still due by the appropriate due date above.
Sole-Proprietorship
Sole-Proprietorship
You must file in Illinois by April 15th.
Applicable R&D Forms
Not eligible
File the above form with the following tax forms:
Form IL-1040 – Individual Income Tax Return
Sole proprietorships report their business income on their individual income tax return using Form IL-1040.
Extension to File Taxes in Illinois for 2024
Taxes owed in Illinois for the tax year 2024 must be paid by April 15, 2025.
No separate extension filing is required in Illinois.
Illinois automatically grants a 6-month extension for individual tax returns.
Sole-Proprietorship: the extension deadline is September 15, 2025.
Note that this extension pertains to the filing deadline, not the payment deadline.
Payment of taxes owed is still due by April 15, 2025.
References
We strive to ensure the accuracy of the information on this page, but it is not intended as tax or legal advice. Please use your own professional judgment and consult with a tax professional. Any advice you provide in connection with tax return preparation must comply in full with the requirements of IRS Circular 230.