Today, ComEd is a unit of Chicago-based Exelon Corporation, one of the nation's largest electric and gas utility holding companies.

[2] The earliest predecessor of Commonwealth Edison was the Isolated Lighting Company, established in early 1881 by George H. Bliss as a subsidiary of Thomas Edison's company to sell small Edison-patented generators and lighting systems, each serving one building or several nearby buildings.

Western Edison installed the first incandescent lighting in a Chicago home, that of stockholder John W. Doane, in 1882, and it was first lit on November 10 of that year.

[4] Chicago Edison's first central generating station, designed by chief engineer Frederick Sargent, opened at 139 (later 120) West Adams Street in August, 1888.

One of Edison's associates, Samuel Insull, had however been retained as the second vice-president of General Electric, and was subsequently offered the presidency of the company.

In reply, Insull applied for the job, saying, "It is the best opportunity that I know of in the United States to develop the business of the production and distribution of electrical energy."

While prevailing opinion at the time held that competition between the many companies was the best way to improve service and keep prices low, Insull believed that a regulated monopoly, giving exclusive operating rights in a specific territory to one company in exchange for state control over service terms and prices, would be most beneficial for both utilities and customers.

While state regulation did not begin until 1914, Insull began forming a monopoly on electric service by acquiring many of his competitors.

By 1895, he had acquired enough of them, and their rights to use the different manufacturers' equipment, that he had obtained a complete monopoly on electric service in Chicago Edison's territory.

[9] Insull also initiated construction of a much larger power plant on Harrison Street, west of the Chicago River.

However, it was left to the individual states to determine the best way to give their electricity customers access to the grid and the benefits of an open market.

For Illinois, the General Assembly passed the Electric Service Customer Choice and Rate Relief Law of 1997.

These rules made it politically desirable for Commonwealth Edison to divest itself of its generation interests, in an attempt to distance itself from any allegations of bias in the competitive process.

It was widely claimed, at the time, that such a dramatic rise in rates was proof that the deregulated environment did nothing to help the consumer and was a sham.

[14] The Illinois General Assembly proposed extending the existing rate freeze for several more years in order to give time to develop a better plan.

[20] On July 17, 2020, ComEd agreed to pay $200 million following what had been a several-year federal investigation of suspected illegal lobbying, political graft and sweetheart contract deals which were made in exchange for the company having a near-monopoly on regional power utility.

ComEd lobbyists wrote the law as mandatory Wireless Smart Meter installations to all customers of Illinois.

When elected, Governor Rauner signed another bill favoring ComEd over the rights of citizens to have a choice to opt out from installation of Wireless Smart Meter.

ComEd and the other primary utility company in Illinois have together installed more than 3 million smart meters—digital devices that collect information about how much electricity is used—at customer homes and businesses.

On February 28, 2018, Illinois utility regulators authorized ComEd to establish a 10-year electric microgrid demonstration project on the South Side of Chicago.