Gov. J.B. Pritzker recently made his case in Crain's for the "fair tax" increase by saying this: "Everywhere I go, I hear a new optimism that Illinois is finally getting on the right path and that our future is brighter."

Perhaps he's been going to Florida, Indiana, Texas and Wisconsin. They're surely giddiest about Illinois' path, because they're taking more of our taxpayers than any other states.

You probably know that Illinois is losing population, but exactly which taxpayers are fleeing and what's the impact? Is it really just low earners leaving, as often claimed? Not big earners who, initially at least, would be the only ones hit by the "fair tax"?

The most direct and current answers come from the IRS, which last month released its interstate migration details for 2018. At Wirepoints, we wrote a series of reports taking a close look at what the IRS data says about Illinois—the loss of taxpayers and income, which income groups are moving and how other states compare. We netted incoming and outgoing numbers.

Unfortunately, Illinois continues to be a national outlier on losing people and the money they earn. While lower-income taxpayers are leaving in larger numbers, all income groups are leaving, and big earners account for the vast majority of lost income. And the income gap between those leaving and those arriving is growing.

Illinois lost 88,000 tax filers, which includes dependents, in 2018. They took with them $5.6 billion in annual adjusted gross income, or AGI.

Tax filers with less than $50,000 of income accounted for 43 percent of those who left, but they were hardly alone. Illinois suffered net losses of taxpayers and their income in all categories reported by the IRS.

However, the overwhelming portion of lost income was due to departure of high earners. Tax filers with incomes over $100,000 accounted for 32 percent of total filers lost in 2018 but 78 percent of lost income. The wealthiest bracket of $200,000 and above, which is a vastly smaller portion of Illinois' population, alone represented 11 percent of lost filers but accounted for 55 percent of lost income.

Perhaps most alarming, the wealth gap between residents leaving and coming to Illinois has more than tripled since 2000. In 2018, the average AGI of those who left was about $85,000, while those who entered the state had incomes of just $66,000.

We are losing taxpayers to most other states, netting gains from just six. The total gain from those six states, however, was trivial—just 667 net residents in 2018.

When measured on per-capita basis, only New York lost more AGI than Illinois in 2018. The biggest per-capita winners were Nevada and Idaho. Illinois' neighbors all suffered far smaller AGI losses than Illinois in 2018.

What's the impact on state coffers? In 2018 alone, we estimated that the $5.6 billion in lost taxable income cost Illinois about $230 million in state income tax revenue. That doesn't include millions in sales, property, gas and other taxes that weren't collected. Further impact would be hard to measure. Departing taxpayers also take with them much of their philanthropic giving, consumer spending, investment dollars and more.

The year 2018 wasn't a fluke. Wirepoints' analysis found Illinois has netted annual AGI losses every year since at least 2000. The losses have piled up year after year, totaling $410 billion from 2000 to 2018.

The conclusion seems to be that there's a particular group of voters that "fair tax" proponents needn't worry about convincing—those with brains in their feet. They're gone.

Mark Glennon is founder of Wirepoints, an independent, nonprofit research and commentary organization.