According to a recent AP article in the Chicago Tribune, a bachelor's degree is worth about $23,000 per year.
"That is the average gap in earnings between adults with bachelor's degrees and those with high school diplomas, according to data from the Census Bureau. College grads made an average of $51,554 in 2004, the most recent figures available, compared with $28,645 for adults with a high school diploma. High school dropouts earned an average of $19,169 and those with advanced college degrees made an average of $78,093."
Pretty amazing, when you think about it.
Scroll all the way down to the end of the article for statistics on the number of individuals with high school diplomas vs. bachelor's degrees, broken down by state. IL is slightly above the national average. I thought it would have been higher.