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.
Trending on WorldAtlas
The Most Dangerous Cities in the World
The Largest Countries in the World
The 10 Largest Cities in the World
The 10 Smallest Countries In The World
The Most Popular Sports in the World
Is the Moon a Planet or a Star?
Why Does Ice Float?
Which Country Has the Most Lakes?
29 Largest Armies In The World