Many know that on January 1, 2015, the temporary increases made to the state’s income tax rates that became law under the Taxpayer Accountability and Budget Stabilization Act of 2011 (TABSA) began to phase-down. On that date, the personal income tax rate declined from 5 percent to 3.75 percent, while the corporate rate went from 7 percent to 5.25 percent. What is not well known is: (i) who benefited most from the cut to the personal income tax rate under TABSA, and (ii) whether or not that tax cut can reasonably be expected to stimulate the Illinois economy. This Issue Brief reveals that the state's highest income earners will benefit disproportionately from the income tax rate phase-down, worsening income inequality and failing to stimulate the state's economy.