Business Tax Deadlines

State filing information

Illinois

Business tax filing in Illinois: state returns, sales tax, other business taxes, and the federal dates that apply everywhere.

checked 2026-09-01Verified against Illinois Department of Revenue. 11 sources.

Corporate income tax return

April 15
Form IL-1120 is due on or before the 15th day of the 4th month following the close of the tax year...

Partnership / S corporation returns

April 15
Partnerships April 15; S corporations March 15

Sales tax return

20th of the following month
sales and use tax · Based on average monthly liability: greater than $200 = monthly; between $50 and $200 = quarterly; less than $50 = annual

Other business taxes

1 tax
Personal Property Replacement Tax

Illinois Department of Revenue

Other business taxes

TaxWho owes itDue
Personal Property Replacement TaxCorporations (2.5% of net income), and partnerships, trusts and S corporations (1.5% of net income)Reported and paid with the entity's income/replacement tax return (IL-1120, IL-1120-ST, IL-1065) on that...

Rules in full

Corporate income tax

Form IL-1120 is due on or before the 15th day of the 4th month following the close of the tax year (for June 30 fiscal year-ends: 15th day of the 3rd month; cooperatives: 15th day of the 9th month). Corporate income tax 7% plus personal property replacement tax 2.5% of net income.

Extension. Automatic extension without filing a form: seven months for non-June 30 year-ends and eight months for June 30 year-ends...

Partnerships and S corporations

Pass-through entity (PTE) tax: for tax years ending on or after December 31, 2021, partnerships (other than publicly traded) and S corporations may elect on Form IL-1065 or IL-1120-ST to pay a 4.95% entity-level tax on net income; quarterly estimated payments required if expected PTE plus replacement tax exceeds $500 (15th day of 4th, 6th, 9th, 12th months).

Sales and use tax

Due date. Form ST-1 is due on or before the 20th day of the month following the end of the reporting period (monthly: 20th of following month; quarterly: 20th of month after quarter; annual: January 20).

Filing frequency. Based on average monthly liability: greater than $200 = monthly; between $50 and $200 = quarterly; less than $50 = annual. IDOR notifies filers of changes.

Thresholds. Monthly > $200 average monthly liability; quarterly $50-$200; annual < $50.

Prepayments. If average monthly liability is $20,000 or more, quarter-monthly payments are required, due the 7th, 15th, 22nd, and last day of the month.

Notes

Illinois keeps partnerships (IL-1065) on the April 15 schedule even though the federal 1065 is due March 15. The Illinois corporate franchise tax (paid-in capital based) is administered by the Secretary of State with the annual report and was not researched here.

What we could not confirm. IDOR's corporate page says the automatic IL-1120 extension is seven months (eight for June 30 year-ends) while Drake's KB says six/seven; the official IDOR statement was used. The IL-1120 Q&A page (62.html) returned only a template, so the corporate due date rests on the corporate.html page plus Drake.

Minimum wage in Illinois

State minimum wage

$15.00
Since January 1, 2025

Next change

No scheduled increase
Set by statute

Tipped and local

Tipped cash wage $9.00
Local ordinances: Chicago $17.05, Cook County (municipalities that have not opted out; unincorporated areas) $15.40

Checked 2026-09-02 against Illinois Department of Labor (IDOL) (Illinois Minimum Wage Law, 820 ILCS 105/1-15 (rate schedule at 105/4); rules at 56 Ill). All scheduled minimum wage increases.

Federal dates that apply in Illinois

  1. NOV2Mon
    Employers (Payroll)
    FUTA deposit, Q3 2026 (if liability exceeds $500)
  2. NOV2Mon
    Employers (Payroll)
    Form 941, Q3 2026 (employer's quarterly return)
  3. NOV16Mon
    Tax-Exempt Organizations
    Form 990 extended return (Form 8868), tax year 2025
  4. DEC15Tue
    C-Corporations
    Q4 2026 corporate estimated tax (Form 1120-W)
  5. JAN15Fri
    Individuals & Sole Proprietors
    Q4 2026 estimated tax payment (Form 1040-ES)
  6. FEB1Mon
    Employers (Payroll)
    FUTA deposit, Q4 2026 (if liability exceeds $500)

All 2026 federal deadlines

Sources

  1. https://tax.illinois.gov/ official
  2. https://tax.illinois.gov/research/taxinformation/income/corporate.html official
  3. https://tax.illinois.gov/research/taxrates/income.html official
  4. https://tax.illinois.gov/questionsandanswers/answer.74.html official
  5. https://tax.illinois.gov/questionsandanswers/answer.93.html official
  6. https://tax.illinois.gov/questionsandanswers/answer.689.html official
  7. https://tax.illinois.gov/research/taxinformation/sales/rot.html official
  8. https://tax.illinois.gov/forms/sales/salesandusetax/st-1-instructions.html official
  9. https://kb.drakesoftware.com/kb/Drake-Tax/10617.htm
  10. https://www.avalara.com/taxrates/en/state-rates/illinois/illinois-sales-tax-guide.html
  11. https://www.taxjar.com/sales-tax/states/illinois

Checked 2026-09-01; researcher confidence 0.90. Corrections with a link to the state's own page: contact@businesstaxdeadlines.com.