Frederick County is located in the western part of the U.S. state of Maryland, bordering the southern border of Pennsylvania and the northeastern border of Virginia. It is a part of the Washington-Baltimore Metropolitan Area, and is often recognized as part of Western Maryland.
The county is home to Catoctin Mountain Park (encompassing the presidential retreat Camp David) and to the U.S. Army's Fort Detrick. The county seat is Frederick, which was home to several celebrated historical figures like Francis Scott Key, Thomas Johnson (governor), Roger B. Taney and Barbara Fritchie. The county may have been named for Frederick Calvert, 6th Baron Baltimore.