331 Area Code — Illinois
331 is a North American Numbering Plan area code for Illinois, the United States. It covers about 1,454,618 people in 46 towns and 78 ZIP codes, including Aurora, Naperville and Schaumburg.
| Field | Value |
|---|---|
| Area code | 331 |
| Country | United States (+1) |
| State / province | Illinois |
| Type | Shares its towns with 630 |
| Time zone | Central |
| Population covered | 1,454,618 |
| Towns covered | 46 |
| ZIP codes | 78 |
| Approx. centre | 41.849, -88.177 |
Where area code 331 is used
Area code 331 is assigned to Illinois, the United States, inside the North American Numbering Plan. Numbers in the code are written (331) NXX-XXXX at home and +1 331 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: 630. 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 331
The 46 towns below are the largest in the 331 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 |
|---|---|---|---|
| Aurora | DuPage County | 186,692 | 10 |
| Naperville | DuPage County | 169,081 | 6 |
| Schaumburg | Cook County | 77,949 | 7 |
| Wheaton | DuPage County | 59,857 | 2 |
| Downers Grove | DuPage County | 57,824 | 2 |
| Saint Charles | Kane County | 56,955 | 2 |
| Lombard | DuPage County | 52,596 | 1 |
| Elmhurst | DuPage County | 47,516 | 1 |
| Oswego | Kendall County | 43,047 | 1 |
| Carol Stream | DuPage County | 42,307 | 6 |
| Bartlett | DuPage County | 41,382 | 1 |
| Glen Ellyn | DuPage County | 38,696 | 2 |
Counties covered
| County | ZIP codes |
|---|---|
| DuPage County | 48 |
| Kane County | 16 |
| Cook County | 8 |
| Kendall County | 4 |
| Will County | 2 |
Other area codes serving the same towns
Nearby area codes
How to dial area code 331
- Within North America: 331 + 7-digit number (331-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 331, then the 7-digit number — for example 00 1 331 NXX-XXXX from most of Europe.
Frequently asked questions
What area code is 331?
331 is a North American Numbering Plan area code assigned to Illinois, the United States. It covers about 1,454,618 people in 46 towns.
Is 331 a US or Canadian area code?
331 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 331 in?
Area code 331 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.