If you’re focused on only the federal estate tax, you may be missing a closer threat. Illinois imposes its own state estate tax with an exemption of just $4 million per person. This is far below the 2026 federal threshold of $15 million.1 For high-net-worth families in Illinois, that gap creates a meaningful planning challenge: You may owe the state a significant tax bill even when you owe nothing to the federal government.
What makes Illinois estate tax planning especially important is the state’s unique structure. The exemption hasn’t been adjusted for inflation since 2012. Illinois offers no portability between spouses, and the state uses a “cliff” tax structure that can produce a disproportionately large bill when the threshold is crossed.2 Understanding these rules is the first step in helping to protect the wealth you’ve built.
Illinois estate tax basics
The tax applies to Illinois residents’ worldwide assets and to nonresidents’ Illinois-based assets, as soon as the total estate exceeds $4 million.
The cliff structure
One of the most important features of Illinois estate tax is its “cliff” structure. Unlike the federal system, which taxes only the amount above the exemption, Illinois taxes the entire estate when it exceeds the $4 million threshold. Being $1 over the exemption doesn’t mean paying tax on $1. It means the full estate becomes taxable.³ For families near the threshold, this distinction can have significant financial consequences.
Rates and calculation
Illinois estate tax rates are graduated, topping out at approximately 16%. The tax is calculated using a legacy federal formula, not a simple rate schedule, which adds complexity to the calculation. Importantly, lifetime taxable gifts may also be included when determining whether the $4 million threshold is reached, so prior gifting activity can affect current estate tax exposure.
No portability between spouses
The federal estate tax system allows a surviving spouse to use their deceased spouse’s unused exemption, a feature called portability. For married couples, this makes coordinated estate planning particularly important.
Illinois does not offer portability. Each spouse has a separate $4 million exemption, and if the first spouse to die doesn’t use theirs through careful planning, it’s lost.
How Illinois’ estate tax compares to the federal estate tax
The 2026 federal estate tax exemption is $15 million per individual, indexed for inflation. The federal system taxes only the amount above the exemption, and it offers portability between spouses. Illinois’ $4 million exemption, by contrast, has not changed since 2012 and offers neither of these features.
That growing gap between federal and state thresholds means that many Illinois families who owe nothing federally can still face a meaningful state tax. For families with estates between $4 million and $15 million, what might be called the “Illinois-only” zone, state-level planning is where the real work may need to happen.
What Illinois counts as a taxable estate
Illinois generally follows the federal definition of a taxable estate. For residents, that means virtually every asset you own is counted, regardless of where it’s located:
- Real estate, including primary residences, vacation homes, and investment properties
- Investment and bank accounts
- Retirement assets
- Life insurance proceeds for policies owned by the decedent
- Business interests
Because the estate includes all worldwide assets for residents, families with significant retirement balances or life insurance coverage sometimes find themselves closer to the $4 million threshold than they expected.
Residents vs. nonresidents: How exposure differs
If you’re an Illinois resident
As a resident, Illinois taxes all assets you own worldwide. Every dollar counts toward the $4 million threshold, which means residents have a higher likelihood of triggering the tax than they might assume. Structuring the ownership of Illinois property and coordinating that with overall estate planning are especially important.
If you’re a nonresident who owns Illinois property
Nonresidents are taxed only on Illinois-based assets: real estate, tangible personal property located in the state, and Illinois-based business interests. Intangible assets, such as stocks and bank accounts, are generally excluded for nonresidents. However, Illinois’ apportionment rule means the tax is calculated on the full estate first, then reduced based on the proportion of Illinois assets.
Because LLC interests are generally treated as intangible property, this structure may help convert what would otherwise be taxable Illinois real estate into an asset that falls outside state estate tax exposure for nonresidents. This approach involves legal and tax considerations and should be reviewed carefully with qualified advisors before implementation.
Illinois estate tax planning strategies for residents
For Illinois residents, the following planning strategies may help reduce estate tax exposure:
Gifting strategies
Illinois does not impose a state gift tax, which creates an opportunity to reduce your taxable estate through lifetime gifts. Strategic gifting not only lowers the estate’s total value but also removes future appreciation of those assets from your estate. Annual exclusion gifts, currently $19,000 per recipient per year for 2026, are a straightforward way to begin.6
Credit shelter trust
Because Illinois doesn’t offer portability, married couples often benefit from a credit shelter trust (also called a bypass trust). By directing the first spouse’s assets, up to the $4 million exemption, into this type of trust, the couple can potentially preserve both spouses’ individual exemptions, sheltering up to $8 million from Illinois estate tax. This requires coordination with an estate planning attorney and should be reviewed as circumstances change.
Irrevocable trusts
Irrevocable trusts, including irrevocable life insurance trusts (ILITs), can remove assets from your taxable estate entirely. An ILIT, for example, can hold life insurance policies so that the death benefit doesn’t count toward your estate. Because these trusts involve a permanent transfer of assets, they require thoughtful planning and should be established well before the need arises.
Illinois estate tax planning strategies for nonresidents
If you’re not an Illinois resident but own property there, your planning focus should be on managing your Illinois-situs exposure:
- Review ownership of Illinois real estate and business interests to understand your current exposure.
- Consider entity planning, such as holding real estate through an LLC, to potentially change how assets are classified for estate tax purposes.
- Evaluate disposition strategies, including selling or gifting Illinois assets during your lifetime.
- Assess exposure early, especially for vacation homes or smaller holdings that may still trigger tax based on overall estate size.
Common planning risks to avoid
Illinois estate tax planning involves a few pitfalls that are easy to miss:
- Assuming you have no Illinois exposure because your estate falls below the federal threshold.
- Failing to plan for the cliff effect, which can produce a disproportionately large tax on estates just over $4 million.
- Underestimating estate value by not accounting for life insurance, retirement accounts, or closely held business interests.
- Lacking coordination between state and federal planning; strategies that work well federally may need adjustment for Illinois.
How Mercer Advisors can help
Illinois’ estate tax rules create meaningful planning complexity, and the gap between federal and state thresholds keeps growing. Both residents and nonresidents can face exposure they didn’t anticipate, and waiting until later in life limits the available options.
At Mercer Advisors, our estate planning specialists work directly with your wealth advisor, tax professionals, and financial planners to evaluate your Illinois estate tax exposure and identify strategies suited to your situation. Whether you’re beginning to think about estate planning or updating an existing plan, we’re here to help you navigate the details.
Not a Mercer Advisors client?
We offer comprehensive wealth management that includes estate planning, tax planning, investment management, and insurance solutions.
-
Illinois imposes a state-level estate tax on estates valued above $4 million. Unlike the federal estate tax, which has a 2026 exemption of $15 million per individual, Illinois’ exemption has not been adjusted for inflation since 2012. The tax is calculated on a graduated schedule with rates up to approximately 16%.
-
No. Illinois does not have an inheritance tax, which means your beneficiaries do not owe tax when they receive assets from your estate. The estate itself, however, may owe Illinois estate tax before assets are distributed.
-
Illinois uses a cliff structure, meaning that as soon as an estate exceeds $4 million, the entire estate — not just the amount above the threshold — becomes subject to tax. This is different from the federal system, which taxes only the amount above the exemption.
-
A credit shelter trust (also called a bypass trust) is often recommended for married Illinois couples because the state doesn’t offer portability between spouses. Without this structure, a surviving spouse may lose the first spouse’s $4 million exemption. A qualified estate planning attorney can determine whether a credit shelter trust is appropriate for your situation.
-
Holding Illinois real estate through an LLC may help nonresidents convert otherwise taxable real property into intangible property that falls outside Illinois estate tax for nonresidents. This strategy involves legal and tax considerations and should be reviewed by a qualified advisor before implementation.
-
Lifetime gifting can be an effective way to reduce your taxable estate because Illinois has no state gift tax. Annual exclusion gifts — currently $19,000 per recipient in 2026 — and larger gifts may reduce your estate’s value and remove future appreciation from your estate. Consult with a tax professional to understand how gifts may affect your overall estate plan.
-
Mercer Advisors estate planning specialists can evaluate your Illinois estate tax exposure and work with your wealth advisor and tax team to identify strategies suited to your situation. You can learn more or schedule a conversation at merceradvisors.com.
-
Illinois estate tax returns are filed with the Illinois Office of the State Treasurer. The return is due within nine months of the decedent’s death. An estate planning attorney or qualified tax advisor can assist with preparation and filing.
-
The two systems differ significantly. The 2026 federal exemption is $15 million per individual, indexed for inflation, and the federal system offers portability between spouses. Illinois’ exemption is $4 million, has not been adjusted for inflation since 2012, and offers no portability. The federal system taxes only the amounts above the exemption; Illinois uses a cliff structure that taxes the entire estate as soon as the threshold is crossed.
-
A trust generally offers more planning flexibility than a will when it comes to Illinois estate tax. A revocable living trust alone doesn’t reduce estate tax, but irrevocable trusts — such as credit shelter trusts or irrevocable life insurance trusts — can help remove assets from the taxable estate or preserve both spouses’ exemptions. The right approach depends on your specific situation and goals.
- “Illinois Estate Tax, Inheritance Tax & Probate Costs.” PlainEstate, May 15, 2026.
- “The $4,000,001 Mistake: How Being $1 Over Illinois’ Estate Tax Threshold Can Cost Your Family Hundreds of Thousands.” Gateville Law Firm, March 9, 2026.
- “The $4,000,001 Mistake: How Being $1 Over Illinois’ Estate Tax Threshold Can Cost Your Family Hundreds of Thousands.” Gateville Law Firm, March 9, 2026.
- “Illinois Estate Tax 2026: $4M Exclusion and Rates.” Brevy, June 4, 2026.
- “2026 Estate Tax Exemption and Planning Considerations.” Faegre Drinker, Jan. 12, 2026.
- “Illinois Estate Tax Exemption: What Evanston Families Need To Know.” Pestinger Law LLC.
All expressions of opinion reflect the judgment of the author as of the date of publication and are subject to change. Some of the research and ratings shown in this presentation come from third parties that are not affiliated with Mercer Advisors. The information is believed to be accurate but is not guaranteed or warranted by Mercer Advisors. Content, research, tools and stock or option symbols are for educational and illustrative purposes only and do not imply a recommendation or solicitation to buy or sell a particular security or to engage in any particular investment strategy.
Mercer Advisors is not a law firm and does not provide legal advice to clients. All Estate planning document preparation and other legal advice are provided through select third parties, with which Mercer Advisors has a contractual relationship. Mercer Advisors Tax Services, LLC, does not provide financial audit, assurance, compilations, or forensic accounting services. Each individual tax situation is unique, depending on complexity, additional fees may apply. Insurance products are provided by Mercer Advisors Insurance Services, LLC (MAIS), which places individual life, disability, long term care coverage, and property and casualty coverage through select insurance companies. Trustee services are offered through select third parties with which a client would sign an additional agreement, and additional fees may apply. Insurance products are provided by Mercer Advisors Insurance Services, LLC (MAIS), which places individual life, disability, long term care coverage, and property and casualty coverage through select insurance companies.
Tax preparation and filing services are provided by Mercer Advisors Tax Services, LLC. Clients will sign a separate agreement when engaging Mercer Advisors Tax Services that defines the services provided and any additional fees that may apply.
