	Under current law, Illinois's state income tax rate is a flat rate of 4.95 percent. A flat income tax, which taxes all income levels at the same rate, is required by the current Illinois state constitution. Illinois is one of 18 U.S. states with a flat income tax or no income tax; 32 other states use graduated income taxes, which tax higher incomes at a higher rate. The last state to switch from a flat state income tax to a graduated state income tax was Connecticut in 1996.