I checked the epidemic list that I have but didnt find a scarlet fever outbreak 1910-1920 in Illinois. Influenza pandemic started about 1916-1919.
Illinois does have some death records prior to 1916. They havea a Pre-1916 death index at www.cyberdriveillinois.com/departments/archives/databases/de...
Also there were death notices in the newspapers prior to 1916. Sometimes they say what the person died of. Successful Searching!