312 Area Code — Illinois
312 is a North American Numbering Plan area code for Illinois, the United States. It covers about 2,795,182 people in 6 towns and 90 ZIP codes, including Chicago, Wheeling and Westmont.
| Field | Value |
|---|---|
| Area code | 312 |
| Country | United States (+1) |
| State / province | Illinois |
| Type | Shares its towns with 773, 872 |
| Time zone | Central |
| Population covered | 2,795,182 |
| Towns covered | 6 |
| ZIP codes | 90 |
| Approx. centre | 41.855, -87.695 |
Where area code 312 is used
Area code 312 is assigned to Illinois, the United States, inside the North American Numbering Plan. Numbers in the code are written (312) NXX-XXXX at home and +1 312 NXX-XXXX when dialled from outside Canada and the United States. Since the NANP moved to 10-digit dialling you must always include the area code, even for a local call.
Other area codes in this footprint: 773, 872. They serve towns in the same territory, so a single street can contain numbers from more than one code. That is normal in the NANP and does not change how you dial.
Towns and cities in area code 312
The 6 towns below are the largest in the 312 footprint, ranked by population. Every one of them links to its own page with the full list of area codes and ZIP codes for that town.
| Town | County | Population | ZIP codes |
|---|---|---|---|
| Chicago | Cook County | 2,694,535 | 84 |
| Wheeling | Cook County | 38,298 | 1 |
| Westmont | DuPage County | 24,231 | 1 |
| Hinsdale | DuPage County | 18,056 | 2 |
| Oak Brook | DuPage County | 10,144 | 1 |
| Clarendon Hills | DuPage County | 9,918 | 1 |
Counties covered
| County | ZIP codes |
|---|---|
| Cook County | 85 |
| DuPage County | 5 |
Other area codes serving the same towns
Nearby area codes
How to dial area code 312
- Within North America: 312 + 7-digit number (312-NXX-XXXX). The leading 1 is optional on a mobile phone and required on most landlines for long-distance.
- From abroad: your country's international prefix, then 1, then 312, then the 7-digit number — for example 00 1 312 NXX-XXXX from most of Europe.
Frequently asked questions
What area code is 312?
312 is a North American Numbering Plan area code assigned to Illinois, the United States. It covers about 2,795,182 people in 6 towns.
Is 312 a US or Canadian area code?
312 is a United States area code. Canada and the United States share the +1 country code, so both are part of the same numbering plan.
What time zone is area code 312 in?
Area code 312 is in the Central time zone.
Do I have to dial 10 digits?
Yes. Every NANP call now requires the area code plus the seven-digit number, even for a local call.