This Illinois compliance calendar collects the state and local dates a small business in Aurora, Naperville or anywhere in Kane, DuPage, Will and Kendall counties needs to track from October 2026 through December 2027: sales tax, withholding, unemployment wage reports, income tax returns and Secretary of State annual reports. The 2026 withholding dates come from the Department of Revenue's Publication 131-D; the 2027 dates apply each agency's stated rule and the same weekend and holiday adjustment to the 2027 calendar, so confirm them when Illinois issues its 2027 publications.
How does Illinois treat weekend and holiday due dates?
For sales tax, the ST-1 instructions say a return due on a weekend or holiday is due the next business day. For withholding, the Department of Revenue's Publication 131-D adjusts for weekends and holidays; for example, the Q3 2026 IL-941 is due Monday, November 2 because October 31 is a Saturday. IDES publishes statutory dates (April 30, July 31, October 31, January 31) without a weekend rule on its page, so file by the preceding Friday when the date falls on a weekend. The 2027 dates below shift weekend and federal holiday dates forward; Illinois will publish its own 2027 withholding publication, which controls.
What does the Illinois compliance calendar show for the rest of 2026?
| Date | Filing | Who |
|---|---|---|
| Tue Oct 20, 2026 (passed) | ST-1 for September and for Q3 2026 | Monthly and quarterly sales tax filers |
| Fri Oct 30, 2026 | IDES Form UI-3/40 for Q3 2026 (statutory date October 31, a Saturday) | Employers |
| Sat Oct 31, 2026 | Remote Retailer Tax Amnesty application closes | Eligible remote retailers |
| Mon Nov 2, 2026 | IL-941 for Q3 2026 | Employers |
| Mon Nov 16, 2026 | IL-501 payment for October withholding | Monthly payers |
| Fri Nov 20, 2026 | ST-1 for October | Monthly sales tax filers |
| Mon Nov 30, 2026 | IDES monthly wage report for October | Employers with 25 or more employees in the prior year |
| Tue Dec 15, 2026 | IL-501 payment for November withholding | Monthly payers |
| Mon Dec 21, 2026 | ST-1 for November (December 20 is a Sunday) | Monthly filers |
| Thu Dec 31, 2026 | IDES monthly wage report for November | Employers with 25 or more employees |
What are the 2027 sales tax and withholding dates?
| Item | 2027 due dates |
|---|---|
| ST-1 monthly (period in parentheses) | Jan 20 (Dec), Feb 22 (Jan), Mar 22 (Feb), Apr 20 (Mar), May 20 (Apr), Jun 21 (May), Jul 20 (Jun), Aug 20 (Jul), Sep 20 (Aug), Oct 20 (Sep), Nov 22 (Oct), Dec 20 (Nov) |
| ST-1 quarterly | Jan 20 (Q4 2026), Apr 20 (Q1), Jul 20 (Q2), Oct 20 (Q3) |
| ST-1 annual | Wednesday, January 20, 2027 (for 2026) |
| IL-941 quarterly return | Q4 2026: Feb 1; Q1: Fri Apr 30; Q2: Mon Aug 2; Q3: Mon Nov 1 |
| IL-501 monthly payments | Jan 15, Feb 16, Mar 15, Apr 15, May 17, Jun 15, Jul 15, Aug 16, Sep 15, Oct 15, Nov 15, Dec 15 |
IDOR assigns your ST-1 frequency from average monthly liability: more than $200 may be monthly, $50 to $200 quarterly, and under $50 annual. New withholding taxpayers start on monthly payments and quarterly returns, and move to semi-weekly if they withhold more than $12,000 in the look-back period or in a quarter. See Illinois sales and use tax registration and filing and Illinois payroll withholding, UI and new hire.
What are the IDES unemployment dates?
| Report | Dates |
|---|---|
| Quarterly UI-3/40 | Jan 31, Apr 30, Jul 31 and Oct 31, 2027 (Jan 31 and Oct 31 are Sundays and Jul 31 is a Saturday: file the prior Friday) |
| Monthly wage reports, employers with 25 or more employees | January report by Feb 28, Feb by Mar 31, Apr by May 31, May by Jun 30, Jul by Aug 31, Aug by Sep 30, Oct by Nov 30, Nov by Dec 31 |
| Extensions | Request before the due date: 30 extra days for quarterly, 15 for monthly |
No monthly report is filed for the last month of a quarter; it is part of the quarterly report. See Illinois employer registrations for the 2026 rates.
What are the Illinois income tax dates for 2027?
| Return | Original due date | Automatic extension |
|---|---|---|
| IL-1040 (individuals) | Thu Apr 15, 2027 | Six months, to Fri Oct 15, 2027 (payment is still due April 15) |
| IL-1040-ES estimates | Jan 15 (2026 Q4), Apr 15, Jun 15, Sep 15, 2027 | n/a |
| IL-1065 (partnerships and LLCs taxed as partnerships) | Thu Apr 15, 2027 | Six months, to Oct 15, 2027 |
| IL-1120-ST (S corporations) | Mon Mar 15, 2027 | Seven months, to Fri Oct 15, 2027 |
| IL-1120 (C corporations) | Thu Apr 15, 2027 | Seven months, to Mon Nov 15, 2027 |
Notice the difference from the federal calendar: a partnership files federal Form 1065 by March 15 but the Illinois IL-1065 by April 15. Pay any expected tax by the original date. For the full federal list use the federal tax calendar 2026-2027.
When is the Illinois LLC annual report due?
The annual report is due before the first day of the entity's anniversary month, and you may file in the 60 days before that date. The pre-filled form arrives about 45 days earlier. The table shows the 2027 window for each anniversary month.
| Anniversary month | File from | File by |
|---|---|---|
| January | Nov 2, 2026 | Dec 31, 2026 |
| February | Dec 3, 2026 | Jan 31, 2027 |
| March | Dec 31, 2026 | Feb 28, 2027 |
| April | Jan 31, 2027 | Mar 31, 2027 |
| May | Mar 2, 2027 | Apr 30, 2027 |
| June | Apr 2, 2027 | May 31, 2027 |
| July | May 2, 2027 | Jun 30, 2027 |
| August | Jun 2, 2027 | Jul 31, 2027 |
| September | Jul 3, 2027 | Aug 31, 2027 |
| October | Aug 2, 2027 | Sep 30, 2027 |
| November | Sep 2, 2027 | Oct 31, 2027 |
| December | Oct 2, 2027 | Nov 30, 2027 |
An LLC's fee is $75 and a delinquent LLC faces a $100 penalty if the report is still missing after the first day of the second month following the anniversary month. Details are in the annual report and registered agent guide.
Which local dates should you add?
Property tax on commercial space is billed a year in arrears: DuPage County's 2025 bills were due June 1 and September 1, 2026, and the county sets the 2026 dates when it mails bills in spring 2027. Check your county treasurer for Kane, Will and Kendall. Aurora licensed businesses renew their city licenses annually, and municipal taxes such as food and beverage tax follow city schedules. Put those dates beside the state ones.
Worked example
Naperville Design Studio LLC (taxed as an S corporation, calendar year, 12 employees) has monthly ST-1 filings for retail sales and monthly IL-501 payments. It files the IDES UI-3/40 for Q3 by October 30, files IL-941 for Q3 by November 2, pays October withholding by November 16 and files ST-1 by November 20. In 2027 it files IL-1120-ST by March 15 and renews the annual report in its anniversary month. It never relies on one calendar for both federal and Illinois dates.
Mistakes to avoid
- Assuming the IL-1065 follows the federal March 15 date.
- Treating the IDES date as moving to Monday without confirming.
- Letting a payroll provider file IL-941 while the ST-1 sits in a separate system.
- Forgetting that an annual report is due before the anniversary month starts, not during it.
- Missing the amnesty window as a remote seller.
How we can help
Our Aurora-area CPA firm maintains Illinois compliance calendars for clients: sales tax, payroll, income tax and annual reports. If you also file in Canada or India, we coordinate with your Canadian CPA or Indian Chartered Accountant so every deadline sits on one calendar. See payroll and employer compliance and sales tax and GST compliance.
Frequently asked questions
When are Illinois sales tax returns due?
On the 20th of the month after the period ends, moved to the next business day if the 20th is a weekend or holiday.
When is the Illinois withholding return due?
Form IL-941 is quarterly. Q3 2026 is due Monday, November 2, 2026, and Q4 2026 is due Monday, February 1, 2027.
When is the Illinois LLC annual report due?
Before the first day of the anniversary month, with a 60-day filing window.
Do Illinois returns automatically get extended?
Yes for IL-1040, IL-1065, IL-1120 and IL-1120-ST, but payment is still due on the original date.
Where do I find official Illinois dates?
The Department of Revenue publishes Publication 131-D each year for withholding; IDES and the Secretary of State publish their own dates.
Official sources
- Illinois Department of Revenue: Publication 131-D, 2026 withholding due dates
- Illinois Department of Revenue: ST-1 instructions
- Illinois Department of Revenue: IL-1065 instructions
- Illinois Department of Revenue: IL-1120-ST instructions
- Illinois Department of Employment Security: Employer tax information
- Illinois Department of Revenue: 2026 Remote Retailer Tax Amnesty
This page summarizes public guidance in plain language. If anything here differs from the official source, the official source controls.
General information only. It is not tax, legal, accounting or immigration advice for your situation, and rules change; confirm the current rules with the official source or a licensed professional in the relevant country.