| District of Illinois area codes: 815 | |
|---|---|
| Country | United States |
| State/Province | Illinois |
| Major City | Chicago |
| Time Zone | Central |
| Prefix | County | Primary City | Company |
|---|---|---|---|
| 815-200 | La Salle | La Salle, IL | Paetec Communications |
| 815-201 | Winnebago | Rockford, IL | Bandwidth.com Clec |
| 815-202 | La Salle | Oglesby, IL | New Cingular Wireless PCS |
| 815-203 | Will | Joliet, IL | Usa Mobility Wireless |
| 815-204 | Mchenry | Crystal Lake, IL | Usa Mobility Wireless |
| 815-205 | Cook | La Grange Park, IL | Centurylink Communications LLC |
| 815-206 | Mchenry | Woodstock, IL | Ameritech Illinois |
| 815-207 | Will | Joliet, IL | AT&T Local |
| 815-208 | Whiteside | Fulton, IL | Mediacom Telephony Of Illinois |
| 815-209 | Winnebago | Rockford, IL | Level 3 Communications |
| 815-210 | Will | Joliet, IL | New Cingular Wireless PCS |
| 815-212 | Will | Joliet, IL | T-mobile Usa |
| 815-213 | Whiteside | Sterling, IL | United States Cellular Corp. - Illinois |
| 815-214 | Kankakee | Kankakee, IL | Rcn Telecom Services Of Illinois |
| 815-215 | Will | New Lenox, IL | First Communications LLC |
| 815-216 | Kankakee | Kankakee, IL | Cellco Partnership DBA Verizon Wireless |
| 815-217 | Dekalb | Dekalb, IL | Digital Network Access Communications |
| 815-218 | Winnebago | Rockford, IL | Cellco Partnership DBA Verizon Wireless |
| 815-219 | Mchenry | Crystal Lake, IL | Sprint Spectrum L.p. |
| 815-220 | La Salle | La Salle, IL | Ameritech Illinois |
There are 785 prefixes, In the code area, the major cities are Belvidere, IL;Crystal Lake, IL;De Kalb, IL;Freepor. The major city is Chicago.