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  5. Area Code 312

Where Is Area Code 312?

Area code 312 is found in the US state of Illinois. Primarily servicing the city of Chicago (population: 36993827), area code 312 covers 1 county of Illinois.

Located in the Central time zone, area code 312 is on the same time as Chicago, IL.

Area code 312 was brought into effect on January 1, 1947.

Map of Illinois with area code 312 highlighted
Location of Area Code 312 and surrounding states.

Counties in Area Code 312

  • Cook.

Most Populous Cities in Area Code 312

City County City Population Time Zone
Chicago Cook 2,699,382 CST

Note: The above list is based off of the top 25 most populous cities in the area code as per 2012 United States Census Bureau estimates.

View all United States Area Codes.

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This page was last updated on July 3, 2015.