DeKalb, IL is currently using an area code overlay in which area codes 779 and 815 serve the same geographic area. The area code overlay which is in use today was put into service on March 17, 2007 when area code 779 was created as an overlay of area code 815. Area code 815 was put into service in 1947 and was one of the four original area codes assigned to Illinois. Ten digit dialing (area code + seven digit number) is necessary because two different homes in the same geographic area can have the same seven digit phone number but each would have a different area code.
In addition to DeKalb, IL area codes 779 and 815 serve a large area of northern Illiois including the larger cities and communities of Crystal Lake, DeKalb, Freeport, Joliet, Kankakee, Loves Park, Machesney Park, McHenry, Rockford, Romeoville and Woodstock, in addition to many smaller communities within the service area.
DeKalb, IL is located in DeKalb County and observes the Central Time Zone.
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