“Everyone’s leaving Chicago for Florida” is a sentence you can hear in any bar in the region. The IRS actually counts — by matching the addresses on tax returns filed in consecutive years — and we pulled its migration files for Cook County, which record about 162,000 people (counted as exemptions on moving returns) leaving in the most recent year published. The three most common destinations, by a wide margin: DuPage County, Will County, and Lake County, Illinois. About 39% of leavers never left Illinois, 34% landed in the five collar counties — and the named Florida counties in the file, the stars of the narrative, account for under 6%.
Cut one: where they actually went
Chart: KCM Desk computation from IRS county-to-county migration data (tax year 2022 filings to 2023 filings). Hover any bar for mover income.
For most households, “leaving Chicago” means a moving truck to Naperville or Joliet, not a one-way flight. The only out-of-state destination that competes with the collar counties is Lake County, Indiana — Hammond, Gary, and the towns just across the state line — which drew 8,061 people. Sun Belt destinations exist in the data (Maricopa, Harris, Dallas), but no single Sun Belt county drew even 2,700 people from Cook that year. (One accounting note: the IRS folds very small flows into regional catch-all rows for privacy, so state totals here mean the counties named in the file.)
Cut two: the door swings both ways
Migration coverage almost always counts exits and forgets entrances. The same files count both: while 100,358 returns moved out of Cook (including moves abroad), 85,178 moved in from elsewhere in the U.S. Here’s the two-way traffic with the top partners:
| County | Left Cook for it | Moved to Cook from it | Cook’s net loss |
|---|---|---|---|
| DuPage, IL | 19,059 | 12,399 | +6,660 |
| Will, IL | 12,890 | 7,548 | +5,342 |
| Lake, IL | 11,713 | 7,323 | +4,390 |
| Lake, IN | 8,061 | 4,730 | +3,331 |
| Kane, IL | 7,041 | 4,235 | +2,806 |
| McHenry, IL | 4,112 | 1,846 | +2,266 |
| Maricopa, AZ | 2,643 | 1,678 | +965 |
| Los Angeles, CA | 2,538 | 2,059 | +479 |
Cook lost people on net to every one of its top partners that year — the honest headline — but the flows in both directions are large. Nearly 12,400 people moved from DuPage into Cook in the same year 19,059 went the other way. The region’s counties trade tens of thousands of residents annually; the net is the small difference between two big numbers.
Cut three: the money — testing “wealth flight”
Because these are tax returns, we can test the second-loudest claim: that the people leaving are the money. The answer — strictly about income, since AGI measures earnings, not net worth — is yes on average, modestly, and not where you think. Returns that left Cook averaged $117.8k in adjusted gross income, against $108.8k for the two million returns filed from unchanged addresses — leavers run about 8% richer than stayers. Arrivals averaged $85.3k, so the county does trade higher-income leavers for lower-income arrivers on average.
But the average hides two completely different migrations wearing the same narrative. Movers from Cook to Lake County, Illinois — the North Shore — averaged $190k per return, and movers to Dallas County averaged $196k. Movers to Lake County, Indiana averaged $57k. The highest-income flows point at the North Shore and Dallas; the largest lower-income flow crosses the Indiana line, where homes and taxes cost less. The data can’t see anyone’s reasons — but it can see that “wealth flight” as a single story flattens what is actually a sorting of very different households into very different exits.
Cut four: how big is this, really?
The denominator nobody prints: 2,048,505 returns were filed from the same Cook County address both years. The 100,358 that moved away amount to about 4.9% of filers — in what our population analysis shows was the tail end of the peak-outflow era. Census estimates since then show the state’s domestic outflow shrinking by nearly three-quarters and the population growing for three straight years. This file is the anatomy of the outflow at its worst recent year, and even then, “mass exodus” meant roughly one filing household in twenty — with the collar counties, not the Sun Belt, as the destination drawing the most of them.
What this data is, and isn’t
IRS migration data counts tax filers: it undercounts students, many seniors, the lowest-income households, and anyone who didn’t file in both years. “People” here means exemptions claimed on moving returns, an approximation of household members. Incomes are adjusted gross income as reported, small flows are suppressed for privacy, and the newest available year is 2022–23 — the IRS releases these on a multi-year lag, so these are the latest county-to-county files the agency has published, not a portrait of this year. Every number above is computed from the two public files linked below, and the math is simple enough to check in a spreadsheet.
Sources & data
- IRS Statistics of Income, county-to-county migration data — outflow and inflow files, tax year 2022 to 2023 (countyoutflow2223.csv, countyinflow2223.csv), retrieved July 17, 2026. Method: county-identified flows for Cook County, IL (FIPS 17031); people = exemptions (n2), households = returns (n1), income = AGI per return; IRS summary rows used for totals and non-migrants.
- KCM Desk — Illinois population trends and components, Census Vintage 2025 (for the years after this file)
Computed by KCM Desk from the files above as of July 17, 2026. The IRS typically releases the next year’s files on a multi-year lag; we’ll update when 2023–24 lands. Spot an error? Corrections come first.