On average, when do fall colors peak across northern Illinois?

Have you noticed leaves on some trees have started to change colors already? A sign of the times as we inch closer to the first day of astronomical autumn which is Monday, September 22nd! 

But it will take some time before northern Illinois gets into prime "leaf peepin" season. Usually around the late-September and early-October time frame, leaves go through moderate changes. 

However, according to EnjoyIllinois.com, peak fall foliage for areas like Rockford, Galena, and Rochelle doesn't arrive until the second and third week of October.