While filing your Illinois tax return for 2015 may seem obsolete, many taxpayers still need to submit or amend older returns for compliance, refunds, or correction purposes. This guide is designed for individuals, sole proprietors, and small business owners who want to accurately understand how to file their Illinois tax return for 2015. Whether you're filing for the first time, correcting an error, or responding to a notice from the Illinois Department of Revenue, following the proper process for this tax year is essential.
Understanding the requirements of the Illinois Income Tax Act for the 2015 tax year can help minimize penalties and ensure your return is processed without delays. Filing accurately matters not only to avoid issues like late fees or audit flags but also to claim any available credits and refunds. The 2015 tax year introduced several significant changes, including a reduced individual tax rate and adjustments to exemption amounts, which may still affect your filing obligations if you haven’t submitted.
This guide walks you through every step, from identifying who needs to file and which forms to use—including Form IL-1040 and key schedules—to submitting your return electronically or by mail. You’ll also learn about estimated payment rules, refund tracking, common mistakes, and special filing considerations for small business owners. If you're unsure where to begin, this guide simplifies the process so you can confidently file—even years after the original tax filing deadline.
Illinois uses a flat income tax system, which means all taxpayers pay the same percentage of their taxable income, regardless of income level. The uniform tax rate for the 2015 tax year was 3.75%, a decrease from the 5% rate used in prior years. Effective January 1, 2015, this change was established under the Illinois Income Tax Act and impacted all individual and small business taxpayers filing for that year.
In addition to the rate adjustment, the standard exemption allowance increased slightly—from $2,125 in 2014 to $2,150 per person in 2015. This exemption helps reduce taxable income and is available to each taxpayer and qualifying dependent. It's important to correctly apply this exemption claimed on your Illinois Form IL-1040 to avoid overpaying or underreporting your liability.
Several public acts passed in 2015 also affected income tax administration, including new identity verification procedures to prevent fraud. These changes led to longer processing times for some electronically filed returns and refund check issuance. Additionally, tax responsibilities for transportation network providers and retailers registered under the Retailers’ Occupation Tax Act and the Service Occupation Tax Act were clarified that year, though most individual filers were unaffected. Understanding these updates ensures that certain taxpayers—especially those filing late or correcting old returns—use the correct forms and calculations for the 2015 tax year.
If you earned income in Illinois during 2015, you may be legally required to file a state tax return under the Illinois Income Tax Act. Full-year Illinois residents must file Form IL-1040 if they were required to file a federal return or if their Illinois base income exceeded the state’s exemption allowance of $2,150 per person for that year. Filing is also necessary to claim a refund for Illinois income tax withheld from your pay, even if your income was below the filing threshold.
Part-year residents and nonresidents who earned income from Illinois sources must also file. If you moved to or from Illinois in 2015, you must report income earned while living there. Nonresidents must file if they earned income from Illinois-based employment, business, or investments that resulted in a state tax liability. The requirement also applies to nonresident purchasers of motor vehicles, who may need to report use tax under the Use Tax Act or the Illinois Vehicle Code, depending on the transaction.
Sole proprietors and small business owners are subject to the same rules as individual filers but must also include income reported on Schedule C of their federal Form 1040. This income flows through to the state return. You may have additional reporting obligations under separate schedules if you operate as a limited liability company (LLC) or partnership. The Illinois Department of Revenue may require returns from certain business types even if no federal filing is required, especially if sales fall under the Retailers’ Occupation Tax Act or related statutes.
To file your Illinois tax return for 2015, you’ll need several key forms and supporting schedules based on your filing status, income type, and credits. The primary form individuals and sole proprietors use is Form IL-1040, the Illinois Individual Income Tax Return. This form is required for all taxpayers filing for 2015, whether you are claiming a refund, reporting income, or responding to a final notice. If you’re submitting a payment by mail, include Form IL-1040-V, the payment voucher. If you’re amending a previously filed return, use Form IL-1040-X.
The following schedules support specific types of deductions, credits, or income adjustments:
If you operate as a business entity other than a sole proprietorship, you may need additional forms:
All these forms must reflect the 2015 tax year and are available on the Illinois Department of Revenue website. Using forms from a different tax year can delay processing or trigger audit flags from IDOR’s audit bureau.
Before completing your Illinois Form IL-1040 for the 2015 tax year, gather all relevant documents to ensure accuracy and avoid delays or requests for additional information from the Illinois Department of Revenue.
Have the following ready:
Completing your return accurately is crucial for avoiding delays, identity verification letters, or rejection notices. The Illinois Department offers walk-up window service at select state facilities if you need in-person assistance. Ensure your return reflects the correct tax year to prevent refund checks or assessment issues.
If you operated as a sole proprietor in 2015, your business income must be reported on Schedule C of your federal Form 1040, which then carries over to Line 1 of your Illinois Form IL-1040. The state treats this business income as part of your return. Still, special considerations under the Illinois Income Tax Act and related laws, such as the Retailers’ Occupation Tax Act and Service Occupation Tax Act, may affect your final tax due.
Business losses reported on Schedule C may offset other income on your Illinois return, reducing your overall tax liability. However, these losses must be calculated and documented correctly. Illinois does not conform to all federal depreciation rules, so adjustments may be necessary on Schedule M to comply with IDOR’s audit bureau standards.
If you earned income from customers or clients in other states while maintaining Illinois residency, you may need to file Schedule CR to claim a credit for taxes paid to other states. Remember that reciprocal agreements with states like Iowa, Wisconsin, Kentucky, and Michigan may affect your filing requirements.
If your business operated as a partnership, S corporation, or limited liability company, you may need to file Form IL-1120-ST or include Schedule K-1-P to report ownership distributions. Also, review Schedule 1299-C to see if you qualify for business-related tax credits, such as those tied to equipment purchases or employment initiatives. Don’t overlook vehicle-related rules, especially if you excluded vehicles subject to use tax or purchased motor vehicles from private parties that may trigger filing under the Use Tax Act.
Failing to follow these small business filing rules could result in penalties, notices from the Informal Conference Board, or future enforcement through the final notice process.
You can file your Illinois tax return for 2015 electronically or on paper, depending on your preference and situation. The Illinois Department of Revenue encourages taxpayers to use electronic filing whenever possible to reduce errors and processing delays. If you're using a MyTax Illinois account, you can file directly through the state’s online platform. It's secure and free and lets you track your return and refund status in real time.
Those eligible for an electronic filing exception, such as individuals with specific paper-only documentation or limited access to technology, may opt to file by mail. In these cases, ensure all required documents are included with your paper return. Attach W-2s, 1099s, and any applicable schedules to avoid receiving a final notice for missing information.
The mailing address depends on whether you expect a refund or are making a payment:
PO Box 19027, Springfield, IL 62794-9027
When mailing your return, use only check payments if paying by mail. Write your Social Security number and tax year in the memo line, including Form IL-1040-V (payment voucher). For those who need in-person help, revenue walk-up windows are available at select state facilities, including Lexington St.
You have several payment options if you owe Illinois income tax for the 2015 tax year. The easiest way is to pay electronically through your MyTax Illinois account or commercial tax software. Electronic payments can be made directly from a checking or savings account. Include your IL-PIN or Social Security Number when submitting payment to ensure it’s applied to your current tax year liabilities.
You may also pay by credit card using one of Illinois' approved third-party payment processors. Note that convenience fees may apply. Certain taxpayers commonly use this method to gain additional flexibility when remitting large balances or making payments from multiple accounts.
If mailing your payment, include a check or money order payable to the Illinois Department of Revenue, and attach Form IL-1040-V. To comply with state guidelines, the department accepts only check payments by mail—cash is not allowed. Payments must be postmarked by the income tax deadline (April 18, 2016, for 2015 returns) to avoid late fees and the estimated payment penalty.
Regardless of the method, keeping a record of your transactions helps if you ever need to respond electronically to future inquiries. Late or incomplete payments may trigger interest, a final notice, or other action by IDOR's collections division. If you need help, visit one of the state's walk-up service locations.
If you expected to owe $500 or more in income tax for the 2016 tax year after subtracting withholding and credits, you must make estimated tax payments using Form IL-1040-ES. This requirement applied to individuals, sole proprietors, and limited liability company members whose income wasn’t subject to regular withholding—such as self-employment income, rental earnings, or interest and dividends.
Failing to make timely payments may result in an estimated payment penalty, which accrues monthly based on unpaid amounts. To avoid penalties, use the payment coupons included with Form IL-1040-ES or submit payments through your MyTax Illinois account. Always indicate the appropriate tax year and quarter when submitting payments.
If your income varies, Illinois allows you to annualize earnings to match when they were earned, helping you minimize penalties. However, the state may reject estimated payment reductions that lack documentation. You can appeal assessments through the Informal Conference Board if needed.
For future planning, remember that certain exceptions apply to farmers and fishermen, and those affected by a public act related to disaster declarations may be eligible for deadline extensions under featured programs announced by the Illinois Department of Revenue.
After you file your 2015 Illinois tax return, you can check your refund status or verify a balance due using several tools provided by the Illinois Department of Revenue. The most straightforward way is to use the “Where’s My Refund?” tool on the tax.illinois.gov website. You can also visit the Illinois Comptroller’s site at myrefund.illinoiscomptroller.gov for additional refund tracking.
To check your refund, you’ll need:
Be aware that delays may occur if your return is flagged for review. In 2015, the state introduced more robust fraud prevention procedures, which could lead to additional verification steps, such as receiving an identity verification letter.
Electronic transactions can be confirmed through your bank or tax software to check payments. For check payments, confirmation is typically available through your financial institution. If there’s a discrepancy or missing record, contact IDOR or visit one of their state facilities, such as the one on Martin Luther King Dr, for support.
If IDOR requires additional information, they might request your response electronically or via mail. Prompt replies help avoid delays in receiving your refund check or resolving outstanding issues tied to your current tax year liabilities.
Before submitting your 2015 Illinois tax return, review this checklist to ensure you’ve completed all required steps and included necessary documentation. A carefully reviewed return helps minimize penalties, avoids unnecessary delays, and reduces the risk of correspondence from the Illinois Department of Revenue.
If you’re unsure how to fix an error, track a delayed refund, or request document clarification, you should contact the Illinois Department directly. They can assist with questions about prior-year forms, adjustment eligibility, or explanations of a balance due. You may also need to reach out if you've received a notice that requires a response or supporting documents.
For paper filers, remember that private parties cannot drop off returns at state facilities without prior approval. If you’re mailing documents or forms such as a drive-away permit, confirm that they comply with the Illinois Vehicle Code and Use Tax Act guidelines.
Also, review any trending forms listed in the Illinois Department of Revenue’s full press release or featured programs list. These reminders can help taxpayers stay informed about updates, such as changes in the hotel operator's occupation tax, the definition of tobacco products, or the types sold.
If you missed the original income tax filing deadline 2015, you should still file your Illinois return as soon as possible. The Illinois Department allows late filing, but penalties and interest may apply to any unpaid tax. Even years later, you may still be eligible for a refund check. Filing promptly helps avoid further action from the Illinois Department of Revenue.
Most 2015 returns must now be filed by mail, as the window for e-filing prior-year returns has closed. However, the Illinois Department of Revenue still processes late paper-filed returns. Use the correct 2015 forms and attach all schedules and documents. If you’re unsure about formatting or requirements, consult featured programs on tax.illinois.gov for archived updates and filing tips.
Many taxpayers miss out on Schedule ICR and Schedule CR credits, such as the K-12 education expense or property tax credit. Some also fail to exclude eligible retirement income under Schedule M. If you're figuring out how to file your 2015 Illinois tax return, reviewing available deductions first can improve accuracy and reduce tax liability.
If you moved during 2015, you are considered a part-year resident. You’ll need to use Schedule NR to report income earned while living in Illinois. The Illinois Department requires clear separation between in-state and out-of-state income. Keep federal documents on hand to support income allocation, and include any supporting forms that reflect your full- or part-year resident status.
If you have lived in Illinois for all of 2015 but have earned income in another state, include all income on your IL-1040 and use Schedule CR to claim a credit for taxes paid elsewhere. The Illinois Department of Revenue has reciprocal agreements with select neighboring states, which may reduce your burden. Always verify if your situation qualifies for those terms under the state’s guidance.
The Illinois Department of Revenue suggests keeping tax documents for at least three years from the date the return was filed or two years from when the tax was paid—whichever is later. However, keep records for seven years or more if your return involves business income, property sales, or audit adjustments. Retaining a copy of your refund check and payment confirmations is also advised for reference.
You can visit the Illinois Department of Revenue website at tax.illinois.gov to access official forms, instructions, and answers about prior-year returns like 2015. The site also highlights featured programs, updates to state tax laws, and contact options if you need help with your return, estimated payments, or understanding a notice.
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