Updated October 2, 2026. Quick answer: Illinois taxes estates above a $4,000,000 exclusion, which is not indexed and not a true exemption. The tax is the pre-2001 federal state death tax credit, limited so that it cannot exceed 40% of the amount over $4,000,000 once the tax itself is deducted. There is no cliff: an estate of $4,000,000 or $4,000,001 owes $0, tax then builds at about 28.6 cents on each added dollar, and a $5,000,000 taxable estate owes $285,714, the figure the Illinois Attorney General’s own estate tax calculator returns.
Naming a beneficiary on a brokerage account or a vehicle title is covered here: transfer-on-death registration in Illinois.
Looking ahead to 2027? The state’s estate tax exemption for deaths in 2027, from its own tax documents: Illinois estate tax exemption 2027.
Inheriting from, or planning for, someone in this state? Whether the state has an inheritance tax, from its own tax documents: Does Illinois have an inheritance tax?.
Put your own estate through the Attorney General’s method: Illinois estate tax calculator.
Probate in the same state: Illinois Probate Cost 2026, Illinois Probate Filing Fee and When Is Probate Required in Illinois? (2026).
2026 exemption: $4,000,000 · Top rate: 16% (effective marginal rate under the pre-2001 federal state death tax credit table) · Key statute: 35 ILCS 405/2(b); 35 ILCS 405/3
Filing deadline and extensions
Illinois Form 700 must be filed with the Attorney General within nine months of the date of death, the same window as federal Form 706. A separate written extension request or Form 700-EXT can extend the filing date, but an extension of time to pay does not stop interest from accruing until payment is made.
No spousal portability
Illinois does not allow a surviving spouse to claim a deceased spouse’s unused exclusion the way federal law permits DSUE portability. Unlike the federal estate tax, Illinois does not offer portability, so when the first spouse dies, their $4 million Illinois exemption is lost forever unless their estate plan is specifically structured to preserve it. A direct read of the statutory definitions in 35 ILCS 405/2 contains no reference to portability or a deceased spouse’s unused exclusion.
The $4 million threshold, precisely
35 ILCS 405/2(b) defines the state tax credit as the full credit calculable under Section 2011 or 2604 of the Internal Revenue Code as in effect on December 31, 2001, recognizing an exclusion amount of $4,000,000 for persons dying on or after January 1, 2013. An estate valued at $3,999,999 owes nothing. An estate valued at $4,000,001 owes $0 in the Attorney General’s calculator, because the tax is limited to 40% of what remains above $4,000,000 after the tax itself is paid. Above that point the tax rises by about 28.6 cents per added dollar: $28,571 at $4,100,000 and $142,857 at $4,500,000. The exclusion is therefore not a true exemption, since every dollar above it is taxed, but it is not a cliff either: the tax starts at zero and builds from there.
Nonresident decedents and Illinois-situs property
Illinois taxes a nonresident’s Illinois real estate and tangible personal property, with an explicit apportionment formula: the tax is the state tax credit reduced by the amount determined by multiplying the state tax credit by the percentage which the gross value of the transferred property not having an Illinois tax situs bears to the gross value of the total transferred property. For a nonresident, only real estate and tangible personal property physically located in Illinois has an Illinois tax situs.
Check how Illinois estate tax affects your plan.
In the Illinois Attorney General’s example, a $5,000,000 estate with all property in Illinois owes $285,714 in Illinois estate tax. The $4,000,000 exclusion is a taxable threshold, and the tax uses an interrelated calculation. Adjusted taxable gifts, deductions and the location of assets can change the result. Coordinate your financial plan with your estate attorney or tax professional.
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The math on a $5,000,000 estate
Tax owed: $285,714. Illinois computes two figures and charges the lower. The first is the credit table: the tax is deducted from the estate before the table is applied, so it is solved by repetition, and for a $5,000,000 estate it settles at $352,158. The second is the federal limit: the tax cannot exceed 40% of the amount by which the estate, less the tax itself, exceeds $4,000,000. Written out, the tax equals 40% of ($5,000,000 minus the tax minus $4,000,000), which solves to 40% of $1,000,000 divided by 1.40, or $285,714. The federal limit is the lower figure, so it governs. The limit is the lower of the two for estates from $4,000,001 up to roughly $5,360,000; above that the credit table is lower and governs (at $6,000,000 it is $456,071, against a limit of $571,429). These figures assume a taxable estate with no adjusted taxable gifts, entered in both fields of the Attorney General’s calculator.
Correction, October 2, 2026: this page and several related guides previously stated that a $5,000,000 estate owes $391,600 and that an estate of $4,000,001 owes about $15,000 to $20,000. That $391,600 is only the first pass of the credit table, before the tax is deducted from the estate and before the federal limit applies. The corrected figures were checked against the Attorney General’s calculator on October 2, 2026.
Honest gaps
The Illinois Attorney General's own PDF fact sheet and Form 700-EXT could not be machine-read for verbatim quotes this session, so statutory text was confirmed via FindLaw's reproduction of the Illinois Compiled Statutes. The exact mechanism married couples use in place of portability, a state-specific QTIP-style election referenced in secondary sources, was not independently verified against primary statutory text this session.
Source note. Read from https://www.illinoisattorneygeneral.gov/Page-Attachments/form700.pdf; https://www.illinoisestatelaw.com/learning-center/illinois-estate-tax/; https://codes.findlaw.com/il/chapter-35-revenue/il-st-sect-35-405-2/; https://codes.findlaw.com/il/chapter-35-revenue/il-st-sect-35-405-3/ on 2026-09-04.
Related: estate tax by state · who actually pays the estate tax · the lifetime gift and estate tax exemption.
Statutory text read at each state's own department of revenue or legislature. General information, not legal or tax advice; exemptions, rates and filing rules change, and a qualified estate or tax professional should confirm the current figures before you rely on them.