EXHIBIT 21

FIRSTENERGY CORP.

LIST OF SUBSIDIARIES OF THE REGISTRANT

As of

December 31, 2023

FirstEnergy Service Company - Incorporated in Ohio

FirstEnergy Transmission, LLC - Organized in Delaware

FirstEnergy Ventures Corp. - Incorporated in Ohio

Jersey Central Power & Light Company - Incorporated in New Jersey

Metropolitan Edison Company1 - Incorporated in Pennsylvania

Monongahela Power Company - Incorporated in Ohio

Ohio Edison Company - Incorporated in Ohio

Pennsylvania Electric Company1 - Incorporated in Pennsylvania

The Cleveland Electric Illuminating Company - Incorporated in Ohio

The Potomac Edison Company - Incorporated in Maryland

The Toledo Edison Company - Incorporated in Ohio

West Penn Power Company1 - Incorporated in Pennsylvania

1 Merged with and into FirstEnergy Pennsylvania Electric Company on January 1, 2024