Area codes in DeKalb, Illinois
DeKalb, Illinois uses 2 area codes — 815 and 779. The main DeKalb area code is 815.
Area codes serving DeKalb
Phone numbers in DeKalb are written as ten digits — for example (815) 555-0190 — and fall in the Central Time zone.
How DeKalb came to have 2 area codes
The original DeKalb area code is 815, in service since 1947. As the area ran low on available numbers, an overlay code was added over the same region for new phone lines: 779 (2007). Existing numbers kept their original code — an overlay never forces anyone to change their number — which is why DeKalb now uses all 2 codes and every local call is dialed with ten digits.
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Frequently asked questions
What is the area code for DeKalb?
The main area code for DeKalb, Illinois is 815. DeKalb is now served by 2 area codes in total: 815, 779.
How many area codes does DeKalb have?
DeKalb has 2 area codes: 815, 779.
Why does DeKalb have more than one area code?
As DeKalb used up the numbers available in its original area code (815, in service since 1947), additional "overlay" codes were added over the same area so new phone numbers could keep being assigned.
How do you dial a DeKalb number?
Dial all 10 digits — the area code (815 or 779) followed by the 7-digit local number. From abroad, dial +1, then the area code and number.
Sourced from the official NANPA (North American Numbering Plan Administrator) numbering database, current as of August 2, 2026. Refreshed monthly.