Most of the attention in the Illinois-to-Florida migration story goes to the income tax. Illinois’s flat 4.95% is a visible annual cost that any high earner can calculate on a spreadsheet. Florida’s 0% is a visible annual saving.
But for a meaningful number of Illinois families — particularly older ones, business-owner families, and families whose wealth has appreciated over decades rather than flowed through a W-2 — the more consequential state tax is the one they will pay exactly once, at the worst possible moment. It is the Illinois estate tax. And for many of these families, it is the single largest state tax they will ever incur.
The estate tax is also the tax that drives the most carefully planned domicile moves. An income tax saving plays out over years. An estate tax saving plays out in a single event, on an estate whose value was built over a lifetime. Getting the domicile question right before that event is worth, in absolute dollars, more than decades of income tax savings for many families.
Here is how the Illinois estate tax works, why it is structurally punitive, and what Florida domicile does about it.
The $4 Million Exemption
Illinois’s estate tax exemption is $4 million per decedent. It was set at $4 million by statute, where it has remained for more than a decade. It is not indexed to inflation.
For context, the federal estate tax exemption in 2026 sits near $15 million per person. An Illinois decedent leaving a $12 million estate owes zero federal estate tax — their estate falls entirely within the federal exemption. But that same estate owes substantial Illinois estate tax on the $8 million above the $4 million state exemption, calculated at graduated rates climbing to 16%.
This gap between the federal and state exemptions is the defining feature of Illinois estate tax planning. A family with a $6 million estate, which at the federal level is unremarkable, is an Illinois estate tax family. A family with a $15 million estate, which is just at the federal exemption, owes Illinois estate tax on roughly $11 million. The Illinois tax is not a supplemental layer on top of a large federal bill — for most affected estates, it is the only estate tax the family owes, and it exists because the state made a deliberate choice to decouple.
Only a handful of states tax estates at this low an exemption threshold. Most states either have no estate tax at all or maintain exemptions closer to the federal level. Illinois sits in a group of roughly a dozen high-estate-tax jurisdictions, and within that group its exemption is on the lower end. Oregon and Massachusetts have historically been similar; several others (Connecticut, New York, Maryland) have exemptions that moved up toward the federal level over the past decade. Illinois did not.
The Rate Structure
The Illinois estate tax rate does not work the way a progressive income tax works. It uses a version of the federal state-death-tax-credit table that existed before 2001, when Congress phased out the federal credit for state estate taxes. Illinois chose to retain that credit structure as the basis for its own independent tax, even after the federal credit disappeared.
The practical result is a graduated tax with brackets that climb from roughly 8% at the lower end to 16% at the top, applied to the taxable estate after the $4 million exemption. The full calculation also involves a “tentative tax” computation that produces effective marginal rates different from the nominal bracket rates. The actual tax owed on a given estate size is not a number most non-Illinois advisors can work out in their heads.
A rough picture of what Illinois estate tax looks like at different estate sizes — for an individual decedent, before any marital deduction planning:
| Taxable Estate | Illinois Estate Tax (approx.) | Effective Rate |
|---|---|---|
| $4 million | $0 | 0% |
| $6 million | ~$285,000 | ~4.8% |
| $10 million | ~$1,030,000 | ~10.3% |
| $15 million | ~$1,875,000 | ~12.5% |
| $25 million | ~$3,540,000 | ~14.2% |
| $50 million | ~$7,740,000 | ~15.5% |
These are approximations based on the statutory tax table applied to a single individual’s estate with no spousal planning, no QTIP elections, and no lifetime gifting offsets. The actual Illinois estate tax for a specific estate depends on the composition of assets, prior taxable gifts, deductions, and any apportionment of tax between Illinois-sitused and non-Illinois-sitused property.
For an Illinois-domiciled decedent, the Illinois estate tax is calculated on the worldwide estate. Real property located outside Illinois, and tangible personal property located outside Illinois, is generally excluded or apportioned. But stocks, bonds, retirement accounts, life insurance (if owned by the decedent), business interests, and other intangible assets are all included in the Illinois taxable estate regardless of where the decedent’s custodian or investment manager is located. The Illinois estate tax follows Illinois domicile, not asset location.
No Portability Between Spouses
The federal estate tax system allows a surviving spouse to “port” the deceased spouse’s unused exemption, effectively combining the two exemptions at the second death. A couple with a combined estate below $30 million, in 2026, can pass the entire amount to heirs federally tax-free even if all assets were titled in one spouse’s name.
Illinois does not offer portability. The Illinois exemption is $4 million per decedent, and the exemption of the first-to-die spouse is lost unless the estate plan captures it through structural planning — typically a credit-shelter trust funded at the first death with up to $4 million of Illinois exemption, separately from the marital deduction.
Credit-shelter trust planning is available, widely understood, and effective when implemented correctly. But it is not automatic. Many older estate plans drafted during periods when the federal exemption was higher than state exemptions were structured to use the full marital deduction at the first death, deferring all estate tax to the second death. In a federal-only analysis, that approach is tax-neutral. In an Illinois analysis, it wastes the $4 million Illinois exemption of the first-to-die spouse entirely.
The result is that couples with $8 million to $15 million estates — substantial, but not obviously wealth-tax-triggering — can lose $600,000 to $1 million in Illinois estate tax at the second death simply because their plan was drafted without Illinois-specific structuring. The planning fix exists, but it requires attention, and it requires an advisor who treats Illinois estate tax as a first-order consideration rather than a federal-level afterthought.
Florida domicile eliminates the portability question entirely. Florida has no state estate tax, so there is no state exemption to port. The federal portability rules apply to the full federal exemption, which is large enough that for most families, structuring around it is optional rather than essential.
What Happens When You Move to Florida
Illinois estate tax is imposed on Illinois-domiciled decedents. If your legal domicile at death is Florida, your estate does not owe Illinois estate tax on intangible assets — regardless of where your brokerage is, where your investment manager sits, or where the LLC operating your family business is registered.
There are two important exceptions worth understanding.
Real property located in Illinois is always Illinois-sitused. If you own a Chicago residence, a Lake Forest home, or Illinois investment real estate at the time of your death as a Florida domiciliary, the value of that real property is subject to Illinois estate tax. The tax is apportioned based on the ratio of Illinois-situs property to the total estate, but the Illinois tax on the Illinois real property itself does not disappear merely because you domiciled in Florida.
Tangible personal property located in Illinois at death. Similarly, if significant valuables — artwork, jewelry, physical collections — are stored in an Illinois property at the time of death, the value of that property can be subject to Illinois estate tax as property located in Illinois.
For families planning around the Illinois estate tax, these two exceptions mean that a full and clean break usually involves more than just a domicile change. It also typically involves selling or restructuring the ownership of Illinois real estate, or accepting that the Illinois real property portion will remain subject to Illinois tax. For families with substantial Illinois real estate, this is a planning conversation with an estate attorney and a CPA who understand both Florida domicile and Illinois sourcing.
For families whose wealth is held primarily in intangible assets — investment portfolios, retirement accounts, business interests, trust interests, partnership holdings — a genuine Florida domicile effectively eliminates Illinois estate tax. The numbers at meaningful estate sizes are large enough to warrant substantial planning attention, and long before the planning attention is warranted, they are large enough to warrant a hard look at moving.
The Numbers That Matter
A family weighing whether Illinois-to-Florida migration is worth the cost and effort of a domicile change should run the numbers on three tax categories separately.
Annual income tax savings. At 4.95% of taxable income, plus the Personal Property Replacement Tax layer for pass-through entity owners, a successful Florida domicile saves roughly 5% to 6.5% of annual income in state tax. For a family with $1 million of annual income, that is $50,000 to $65,000 per year.
Annual property tax differential. A high-end Illinois home produces an effective property tax of roughly 2% to 2.5% of market value. A comparable Florida home, with homestead exemption, produces an effective rate closer to 0.8%. For a family moving from a $3 million Illinois home to a $3 million Florida home, the annual property tax saving is roughly $30,000 to $50,000.
One-time estate tax savings. For a family with a $10 million estate, Florida domicile saves approximately $1 million at death. For a $25 million estate, approximately $3.5 million. For a $50 million estate, approximately $7.7 million. These savings are denominated in lifetime terms, not annual, but they are the largest single numbers in the analysis.
The total lifetime tax cost of remaining Illinois-domiciled, for a family whose net worth at death will be in the double-digit millions, is typically higher than the lifetime income tax cost alone would suggest. The estate tax is the quiet compounding factor — and it is the one most commonly overlooked when families run the “is it worth moving” calculation.
The Planning Before the Move
For a family considering the move because of the estate tax specifically, a few pre-move steps are worth attention with the right estate attorney.
Basis step-up and appreciated assets. If you plan to sell appreciated assets shortly after the move, consider whether the gain is better realized before establishing Florida domicile (to use whatever basis situation works) or after (to avoid Illinois income tax on the gain). This is a situation-specific analysis and the right answer depends on the asset, the time horizon, and the size of the embedded gain. For most families with large embedded gains, waiting until Florida domicile is established is the better answer — but “established” here means genuinely established, not merely claimed.
Trust structuring. Revocable living trusts drafted for Illinois domicile should generally be reviewed after a Florida move to ensure they reflect Florida law on matters of homestead, creditor protection, and spousal rights. Irrevocable trusts are more complex — an Illinois-situs irrevocable trust with Illinois trustees and Illinois assets may continue to have Illinois tax exposure even after the settlor establishes Florida domicile, depending on the trust’s structure.
Gifting runway. For families approaching the Illinois exemption, annual gifting and lifetime gifting using federal exemption can reduce the Illinois taxable estate over time. This planning is most effective when combined with domicile planning rather than as a substitute for it.
Real estate disposition. If the plan is to keep a secondary home in Illinois after the move, understand that the Illinois real property value will remain exposed to Illinois estate tax at death. If the plan is to dispose of Illinois real estate as part of the move, the timing of the sale relative to the domicile change matters for income tax purposes.
These are conversations with an estate attorney and CPA who work on Illinois estate tax regularly. The decisions are fact-specific, and the stakes are high enough that generalized advice — including this post — is a starting point, not a plan.
The Domicile Standard
Illinois applies a standard domicile test to determine whether a former resident has genuinely departed. The Department of Revenue looks at the totality of the facts: the location of the primary residence, driver’s license and vehicle registration, voter registration, professional relationships, medical providers, religious and social affiliations, family location, location of personal valuables, and — critically — where the decedent actually spent their time.
For estate tax purposes, the domicile question arises at death. The analysis is retrospective, looking back at the facts as of the date of death. A decedent who lived in Florida for ten months of the year and spent two months at an Illinois summer home will generally be considered Florida-domiciled if the underlying facts support it. A decedent who spent six months in Florida, six months in Illinois, kept most of their medical care and social life in Illinois, and maintained Illinois as their “real” home will generally be considered Illinois-domiciled regardless of which Florida paperwork was filed.
The question of how much time was spent where — and in which state — is a factual question resolved by records. Day counts, location documentation, travel history. For an estate tax audit arising after death, this record is being assembled by the executor and by the decedent’s surviving family, often from incomplete or reconstructed sources. Good contemporaneous records make this process straightforward. Poor records make it an expensive fight.
How Southbound Fits
The Illinois estate tax is a one-time event measured in years of documentation. Unlike income tax, which is reset annually, the estate tax question is resolved based on a single answer at a single point in time: was the decedent genuinely domiciled in Florida?
The documentation for that answer is built during the decedent’s life. A contemporaneous, GPS-verified record of where the person spent their days — built passively, without discipline or manual effort, starting from the date of the claimed move — is exactly the kind of evidence that supports a clean answer under Department of Revenue review.
Southbound runs in the background on iPhone. It uses iOS’s significant-location-change system to log whether each day is spent in Florida or outside it. The app is passive and battery-efficient. There are no manual check-ins, no required habits, and no ongoing cost to the user beyond installing it once.
Location data is stored in the user’s personal iCloud account. Southbound has no servers storing location history. We cannot see your data. Years from now, when a probate attorney or an executor needs to produce documentation of where the decedent was genuinely living, that record is available, exportable, and in a form that reflects what it actually is: contemporaneous evidence created in the normal course of life.
For families planning a Florida domicile move with the Illinois estate tax in mind, the day count matters not just in the year of the move but in every year that follows. The record needs to be continuous. Most people cannot produce a continuous record from memory. A passive app does it for them.
This post is for general informational purposes only and does not constitute tax or legal advice. Illinois estate tax planning involves complex, fact-specific legal questions and interacts with federal tax law, state residency law, and trust and estate law. Work with a qualified estate attorney and CPA who specialize in Illinois estate tax and interstate domicile planning before making decisions based on the information above.
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Published Apr 17, 2026