Frederick County, Maryland Frederick County, Maryland Frederick County is located in the northern part of the U.S. state of Maryland. As of the 2010 U.S. Census, the population was 240,336. The county seat is Frederick. Frederick County is included in the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area. Like other outlying sections of the Washington metropolitan area, Frederick County has experienced a rapid population increase in recent years. It borders the southern border of Pennsylvania and the northeastern border of Virginia. The county is home to Catoctin Mountain Park (encompassing the presidential retreat Camp David) and to the U.S. Army's Fort Detrick. It has also
Maryland Route 4 Maryland Route 4 Maryland Route 4 (MD 4) is a state highway in the U.S. state of Maryland. The highway runs from MD 5 in Leonardtown north to Southern Avenue in Suitland at the District of Columbia boundary, beyond which the highway continues into Washington as Pennsylvania Avenue. MD 4 is a four- to six-lane highway that connects Washington and communities around the Capital Beltway (Interstate 95 and I-495) with southern Prince George's County with southwestern Anne Arundel County. The highway is the primary highway for the length of Calvert County, during most of which the route runs concurrently with