Please visit http://research.stlouisfed.org/fred2/personalincome for documentation on the derivation of personal income.
Source: US. Bureau of Economic Analysis
Release: State Personal Income (Quarterly)
US. Bureau of Economic Analysis, Net Earnings by Place of Residence in Illinois [ILENET], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/ILENET, May 2, 2016.