| Area Code | 815 |
| State | Illinois |
| Current Time in Area Code 815 | 815> CDT |
| Timezone | Central Daylight Time |
| Regional Market Area | Champaign and Springfield Decatur Area Davenport-Rock Island-Moline Area Metro Chicago Peoria-Bloomington Area Rockford Area |
| Metro Area(s) | Dixon, IL Freeport, IL Kankakee, IL Ottawa, IL Pontiac, IL Rochelle, IL Rockford, IL Sterling, IL |
| Population (2020) | 2041259 |
| Adjacent Area Codes | 217,219,224,262,309,331,447,464,563,608,630,708,765,779,847 |
| Overlay Area Codes | 779 |
| Crystal Lake |
| DeKalb |
| Joliet |
| Plainfield |
| Rockford |
| Romeoville |