Area code 779 is for northern Illinois, except for the Chicago metro area. It was put into service on March 17, 2007. This is an overlay code that is part of the complex 815/779 combination.
Illinois Counties within Area Code 779:
Boone, Bureau, Carroll, DeKalb, Ford, Grundy, Henry, Iroquois, Jo Daviess, Kane, Kankakee, Kendall, La Salle, Lee, Livingston, Marshall, McHenry, McLean, Ogle, Putnam, Stephenson, Whiteside Count, Will , and Winnebago.
Illinois Major Cities within Area Code 779:
northern Illiois, Crystal Lake, DeKalb, Freeport, Joliet, Kankakee, Loves Park, Machesney Park, McHenry, Rockford, Romeoville and Woodstock.
Area Code 779 Time Zone?
Central time zone is also known as America/Chicago.
Go here to see the complete list of United States Area Codes.