United States. Bureau of Labor Statistics. "Illinois," in United States. Bureau of Labor Statistics. "Employment, Hours, and Earnings, States and Areas, 1972-87 : Bulletin of the United States Bureau of Labor Statistics, No. 2320," Employment, Hours, and Earnings, States and Areas (March 1989) : 11-217. https://fraser.stlouisfed.org/title/245/item/5876/content/pdf/bls_eestates_1972to1987_v2/toc/400041 , accessed on September 10, 2024.