After Prohibition ended in 1933, Illinois changed the drinking age to 21 for men and 18 for women. In 1961, Illinois raised the drinking age to 21 for everyone. In 1973, the drinking age for beer and wine was lowered to 19. In 1980, it was raised back to 21.
According to DrinkingMap.com, Illinois lowered the drinking age to 19 for beer and wine in 1973 as a response to the 26th Amendment, which lowered the voting age to 18. The lowering of the drinking age resulted in an increase in alcohol-related car accidents and deaths, so the Illinois legislature raised the legal drinking age back to 21.