| General Information about Area Code 331 | |
|---|---|
| Country | United States |
| State / Province / Territory | Illinois |
| Major City | Lombard |
| Time Zone | Central (UTC-06:00) |
| Prefix | Primary City | County | Phone Type |
|---|---|---|---|
| 331-725 | Oswego | Kendall | Landline |
| 331-999 | Oswego | Kendall | Landline |
| 331-234 | Sugar Grove | Kane | Wireless |
| 331-321 | Dupage | Dupage | - |
| 331-214 | Downers Grove | Dupage | Wireless |
| 331-221 | Elmhurst | Dupage | Landline |
| 331-253 | Homer Glen | Will | Wireless |
| 331-645 | Elmhurst | Dupage | Wireless |
| 331-281 | Naperville | Dupage | Landline |
| 331-472 | Naperville | Dupage | Wireless |
| 331-200 | Hanover Park | Cook | Wireless |
| 331-777 | Downers Grove | Dupage | Landline |
| 331-481 | Downers Grove | Dupage | Wireless |
| 331-210 | Geneva | Kane | Landline |
| 331-228 | Geneva | Kane | Wireless |
| 331-684 | Aurora | Kane | Landline |
| 331-456 | Roselle | Dupage | Landline |
| 331-305 | Naperville | Dupage | Wireless |
| 331-702 | Naperville | Dupage | Landline |
| 331-251 | Downers Grove | Dupage | Wireless |