Area Codes
| 815 | Illinois (La Salle, De Kalb, Rockford, Freeport and northern Illinois including parts of the Chicago area such as Joliet, Plainfield and Crystal Lake, and is overlaid by 779) | More information at: Area Code 815 Phone Number Blocks
| 815 | Illinois (La Salle, De Kalb, Rockford, Freeport and northern Illinois including parts of the Chicago area such as Joliet, Plainfield and Crystal Lake, and is overlaid by 779) | More information at: Area Code 815 Phone Number Blocks