Located in the Central (GMT -06:00) time zone. Area code 773 serves the state of Illinois. This area code was assigned on February 29th, 1996. On October 12th, 1996 it went into service. 773 is a General Purpose Code. 773 service area does overlap with 872 area codes. Dialing pattern for local calls within the same NPA (area code) is 1+10D.