McHenry, Illinois, has been in area code 815 since the introduction of the original area code system in 1947.
On March 17, 2007, area code 779 was added as an overlay on 815.
Zip code 60012 is applicable for Crystal Lake and Bull Valley, Illinois, which are in McHenry County.
Bourbonnais, Illinois, is in area code 815 and overlay code 779.
There is more than one area code. See link for Illinois area codes.
St. Charles, Illinois, changed from area code 708 to 630 in 1996.St. Charles was in area code 312 until the 312/708 split in 1989.
Olympia Fields, Illinois, is in area code 708.
Bloomington/Normal, IL, is in area code 309.
Oak Brook, Illinois, is in area code 630 and overlay code 331.
Oswego, Illinois, is in area code 630, with overlay code 331. Oswego, Kansas, is in area code 620. Oswego, New York, is in area code 315.
The 847 area code belongs to the state of Illinois. Some of the areas that are covered by the 847 area code also overlap with the 224 area code. This area code is in the upper northeast part of the state.
217 is an Illinois number
Aurora, Naperville, Illinois.
Many cities in Illinois, USA including Rockford and Joliet.