Commonwealth Edison, commonly known as ComEd, is the largest electric utility in Illinois, serving the Chicago and Northern Illinois area. The service territory roughly borders in Iroquois County to the south, the Wisconsin border to the north, the Iowa border to the west, and the Indiana border to the east.

For more than 100 years, Commonwealth Edison has been the primary electric delivery services company for Northern Illinois. Today, ComEd is a unit of Chicago-based Exelon Corporation (NYSE: EXC), one of the nation's largest electric and gas utility holding companies. ComEd provides electric service to more than 3.8 million customers across Northern Illinois.

Commonwealth Edison's transmission lines operate at voltages of 69,000, 138,000, 345,000, and 765,000 volts, delivering power to their 3.8 million customer base. ComEd's subtransmission voltage is 34,500 volts. Their distribution line voltages are 4,160 volts, 7,200/12,470 volts and 7,970/13,800 volts. The company's revenues total more than $15 billion annually.