Illinois Estate Tax Forms & Deadlines
Last updated: 10 Nov 2025 • Author: Alexander Foelsche CPA (US), WP (DE), RE (CH)
Illinois Estate Tax — Forms & Deadlines
One-stop page for Illinois estate tax filing: who must file, which forms you need, due dates & extensions, payment, and checklists. Illinois returns are filed with the Attorney General; tax is paid to the Illinois State Treasurer.
Who must file?
Core forms & where to get them
Illinois forms
- Form 700 — Illinois Estate & GST Tax Return (incl. IL-only QTIP schedules). Download
- Form 700-EXT — Request for extension to file (and payment instructions). Download
- AG Estate Taxes hub — Forms, calculator, fact sheets. Open page
- Estate Tax Payment Form — State Treasurer remittance. Payment page
Federal references to attach
- IRS Form 706 pages/schedules (or pro-forma if no federal filing), and Forms 712 (life insurance).
- Wills/trusts, appraisals, deeds, and valuation support per AG checklist.
See Form 700 instructions and the AG fact sheet for the full attachment list.
Deadlines, extensions & installments
| Item | When due | Notes |
|---|---|---|
| Illinois Form 700 | 9 months after date of death | Illinois follows the federal 9-month rule; file with the AG. |
| Extension to file | ≈ 6 months (typical) | AG recognizes IRS Form 4768 approval; or file Form 700-EXT by the original due date. Time to pay is not extended. |
| Payment of tax | By the 9-month due date | Remit to the Illinois State Treasurer using the Treasurer’s Estate Tax payment process. |
| Installments / deferral | With return/election | If federal IRC § 6166 applies, Illinois generally aligns proportionally for Illinois-situs business property. |
How to file & pay
Where to file
File Form 700 with the Illinois Attorney General (see the form PDFs/web for addresses). Keep proof of mailing/receipt.
How to pay
Send payment to the Illinois State Treasurer via the Treasurer’s Estate Tax payment page/form. Retain confirmations; refunds are issued by the Treasurer to the estate representative.
Practical checklists
Before filing
- Confirm residency; map Illinois-situs vs. non-Illinois assets.
- Complete federal-style schedules (706/pro-forma) and appraisals.
- Evaluate an Illinois-only QTIP election (Form 700 statement & schedules).
When extending
- Request federal extension on IRS Form 4768 (attach approval) or submit Form 700-EXT to the AG by the original due date.
- Remit expected tax to the State Treasurer by 9 months and retain proof of payment.
FAQs
When is Illinois Form 700 due?
Nine months after the date of death. File with the Attorney General; payment goes to the State Treasurer.
Does Illinois accept the federal extension?
Yes. The AG recognizes IRS Form 4768 approvals; or request an Illinois extension via Form 700-EXT. Extensions to file do not extend time to pay.
Where do I send payment?
To the Illinois State Treasurer using the Treasurer’s Estate Tax payment instructions.
What if no federal 706 is required?
You may still need to file Illinois Form 700 if the Illinois threshold is exceeded; attach federal-style schedules and appraisals.