Area code 312 was brought into effect on January 1, 1947.
Counties in Area Code 312
Most Populous Cities in Area Code 312
|City||County||City Population||Time Zone|
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.
This page was last updated on July 3, 2015.