| District of Illinois area codes: 312 | |
|---|---|
| Country | United States |
| State/Province | Illinois |
| Major City | Chicago |
| Time Zone | Central (UTC-06:00) |
| Prefix | County | Primary City | Company |
|---|---|---|---|
| 312-455 | Cook | Chicago, IL | Ameritech Illinois |
| 312-456 | Cook | Chicago, IL | Ameritech Illinois |
| 312-457 | Cook | Chicago, IL | American Messaging (am) |
| 312-458 | Cook | Chicago, IL | Ameritech Illinois |
| 312-459 | Cook | Chicago, IL | T-mobile Usa |
| 312-460 | Cook | Chicago, IL | Ameritech Illinois |
| 312-461 | Cook | Chicago, IL | Ameritech Illinois |
| 312-462 | Cook | Chicago, IL | Ameritech Illinois |
| 312-463 | Cook | Chicago, IL | Ameritech Illinois |
| 312-464 | Cook | Chicago, IL | Ameritech Illinois |
| 312-465 | Cook | Chicago, IL | Us Xchange Of Illinois LLC DBA Choice One Comm Il |
| 312-466 | Cook | Chicago, IL | Ameritech Illinois |
| 312-467 | Cook | Chicago, IL | Ameritech Illinois |
| 312-469 | Cook | Chicago, IL | Ameritech Illinois |
| 312-470 | Cook | Chicago, IL | Mcimetro Access Transmission Services LLC |
| 312-472 | Cook | Chicago, IL | Ameritech Illinois |
| 312-473 | Cook | Chicago, IL | Ymax Communications Corp. |
| 312-474 | Cook | Chicago, IL | Ameritech Illinois |
| 312-475 | Cook | Chicago, IL | Ameritech Illinois |
| 312-476 | Cook | Chicago, IL | Sprint Spectrum L.p. |
There are 701 prefixes, In the code area, the major cities are Chicago, IL. The major city is Chicago.