Frederick County is a county 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 and the presidential retreat Camp David. The county seat is Frederick, which was home to several celebrated historical figures like Francis Scott Key. The county was named for Frederick Calvert, 6th Baron Baltimore.

As of the census˛ of 2000, there were 195,277 people, 70,060 households, and 51,914 families residing in the county. The population density was 114/km˛ (295/mi˛). There were 73,017 housing units at an average density of 43/km˛ (110/mi˛). The racial makeup of the county was 89.33% White, 6.36% Black or African American, 0.21% Native American, 1.67% Asian, 0.03% Pacific Islander, 0.92% from other races, and 1.47% from two or more races. 2.39% of the population were Hispanic or Latino of any race.