The Center for Budget and Policy Priorities, in conjunction with the Economic Policy Institute, has a new report on changes among income by class in America, with state-by-state breakdowns. Illinois's is sobering:

Illinois income inequality

The changing gap between the top and the bottom has been high in Illinois by every timeframe the report measures. The gap between the middle 20 percent in Illinois and the top did not grow as much in recent years as in some other states, but it grew a lot from the 1990s to the mid-2000s, and from the 1970s to the mid-2000s. It's a trend that puts immense pressure on the state's social-safety net, one reason there have been many (unheeded) calls to switch the state's income tax system from a flat tax to a progressive tax.