Monongahela Power Company has its roots in Fairmont. In the summer of 1890, Fairmont Electric Light and Power began operating a 30-kilowatt plant on the Monongahela River, providing the city with electric lights. By 1900, the Schmulbach brewing interests of Wheeling acquired control of Fairmont Electric and built Fairmont's first electric streetcar line. A second plant with a capacity of 210 kilowatts was built. In 1903, local businessmen bought the company back and incorporated it as the Fairmont and Clarksburg Traction Company.

As demand for lighting and other purposes supplanted electric streetcars as the major market for electricity, the company name and corporate strategy continued to evolve. In 1921, the company changed its name to Monongahela Power and Railway Company. Two years later, it was renamed Monongahela West Penn Public Service Company. The company continued to grow through acquisition and expansion, serving an increasing number of customers as the demand for electricity rose. By 1944, the company was completely out of the streetcar business, and in 1945 the corporate name was changed to Monongahela Power Company.

Monongahela Power is part of Allegheny Power, which was owned until 2011 by Allegheny Energy, based in Greensburg, Pennsylvania. In 2011, Allegheny Energy was purchased by FirstEnergy Corporation of Akron, Ohio. The company is now known as Mon Power.

American Electric Power and Allegheny Energy were partners in a project called the Potomac-Appalachian Transmission Highline (PATH). The companies planned to build a 280-mile high-voltage power line that would start near the John Amos Plant in Putnam County and cross a dozen West Virginia counties, as well as parts of Virginia and Maryland. The PATH project was put on hold while additional studies were completed of the potential demand for power that would be provided by the transmission line. Based on those studies, the project was suspended in 2011 and officially removed from future plans in 2012.