7 Reasons an Illinois Estate Pays State Tax When It Owes the IRS Nothing

Illinois’s estate tax law, formally 35 Illinois Compiled Statutes (ILCS) 405, taxes any estate worth more than $4,000,000.

The Internal Revenue Service (IRS) doesn’t ask for a cent until an estate passes $15,000,000 in 2026.

That gap is enormous.

These are the reasons an Illinois estate pays state tax when it owes the IRS nothing.

Note: This is general information, not tax or legal advice. Estate tax rules, exemption amounts, and elections are subject to change.

1. No Portability for Spouses

The state doesn’t let a surviving spouse pick up any unused piece of a spouse’s exemption.

Federal law does the opposite: A widow or widower can carry over whatever exemption the first spouse never used.

The state skips that step.

Picture a couple with a combined $6,000,000 estate, split evenly between them.

If the husband dies first and leaves everything to his wife, his $4,000,000 exemption goes unused and disappears.

Illinois taxes everything above her $4,000,000 exemption when she dies, not the $8,000,000 a portable rule would have allowed.

2. Illinois’s Separate QTIP Election

Illinois lets an estate make a qualified terminable interest property (QTIP) election, separate from any federal QTIP election on the same return.

The election defers Illinois tax on the marital share until the second spouse dies, instead of taxing it right away.

Nothing forces an executor to file it.

An executor who files only the federal QTIP election and skips the Illinois one leaves the first spouse’s exemption to go to waste.

Unlike the automatic portability gap in the first reason, this loss comes down to one form nobody filed.

The election itself has been on the books since 2009.

A family working with an estate attorney who never raises it is missing a tool built exactly for this problem.

3. The Joint Property Trap

Illinois estates run into a federal rule that many families never see coming: Joint ownership doesn’t remove an asset from the estate.

Add an adult child’s name to a bank account or a deed “for convenience,” and the whole thing can still count in the parent’s estate.

That’s true unless the survivor can prove they paid into it themselves.

For a married couple, federal law asks for less.

It automatically counts only half of a jointly owned account or property in the first spouse’s estate, no matter who paid for it.

Non-spouses get no such break.

A sibling added to a family cottage’s deed, or a friend added to a bank account for bill-paying help, can pull the full value into the decedent’s taxable estate.

That’s how this rule can push a family across Illinois’s $4,000,000 line while the same estate stays nowhere near the federal government’s $15,000,000 threshold.

A $900,000 cottage, with a sibling added to the deed, can count at its full value and turn a $3,300,000 estate into a $4,200,000 estate that Illinois taxes.

4. The Life Insurance Add-Back

An Illinois estate counts life insurance at full value, even though the payout itself reaches a beneficiary free of income tax.

That surprises many families.

Federal law includes a life insurance payout in the policyholder’s estate whenever that person held any control over the policy.

That includes the right to change the beneficiary or borrow against the policy.

So a $1,000,000 policy meant to help the kids skip probate can be the exact amount that pushes an otherwise $3,500,000 estate over Illinois’s $4,000,000 line.

5. Retirement Accounts at Full Value

Illinois values an estate’s retirement account at its full pre-tax balance, with no discount for the income tax a beneficiary will eventually owe.

A $500,000 traditional individual retirement account (IRA) shows up as $500,000 on the estate tax return.

The government will still collect income tax later on every dollar the beneficiary withdraws.

The estate gets no credit for that.

A retiree who spent decades maxing out a 401(k) can leave a bigger estate than the family expects.

Add a paid-off house and a modest brokerage account, and the total can cross Illinois’s $4,000,000 line while staying nowhere near the federal government’s $15,000,000 threshold.

6. Farmland and Business Value

Illinois values a family farm or a closely-held business at fair market value for estate tax purposes, the same as a bank account or a stock portfolio.

It doesn’t matter that the land can’t be sold off in pieces to pay the tax bill.

A business’s value works the same way, locked into equipment and inventory instead of cash, and it counts against the estate just as much as the farm does.

A farm worth $4,500,000 on paper, much of it in land and machinery, can trigger an Illinois tax bill.

The family often has to pay that bill in cash, even when the estate holds almost none.

A special valuation rule can lower the taxable number for working farmland, but only when the estate applies for it before the return is due.

7. Property in Other States

Illinois's tax formula starts by treating a decedent's whole estate as Illinois property, then applies a ratio for anything held elsewhere.

That means the total size of an estate, wherever the property sits, decides whether a family crosses Illinois's $4,000,000 line in the first place.

Location alone doesn't save you.

A retiree who splits time between a Chicago condo and a second home in another state can't assume the out-of-state property is invisible to Illinois.

Say half the estate sits in Illinois and half in Florida.

Illinois taxes only its half.