Frederick County is located in the northern part of the U.S. state of Maryland. As of the 2020 U.S. census, the population was 271,717. The county seat is Frederick. Frederick County is part of 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. Catoctin Mountain Park in the county is the location of Camp David, a U.S. presidential retreat, and Fort Detrick, a U.S. Army base. Etymology The namesake of Frederick County and its county seat is unknown, but it was probably either Frederick, Prince of Wales, or Frederick Calvert, 6th Baron Baltimore. History Frederick County was created in 1748 by the Province of Maryland from parts of Prince George's County and Baltimore County. In 1776, following US independence, Frederick County was divided into three parts. The westernmost portion became Washington County, named after George Washington, the southernmost portion became Montgomery County, named after another Revolutionary War general, Richard Montgomery. The northern portion remained Frederick County. In 1837, a part of Frederick County was combined with a part of Baltimore County to form Carroll County which is east of current day Frederick County. The county has a number of properties on the National Register of Historic Places. Geography According to the U.S. Census Bureau, the county has a total area of , of which is land and (1.1%) is water. It is the largest county in Maryland in terms of land area. Frederick County straddles the boundary between the Piedmont Plateau Region and the Appalachian Mountains. The county's two prominent ridges, Catoctin Mountain and South Mountain, form an extension of the Blue Ridge. The Middletown Valley lies between them. Attractions in the Frederick area include the Clustered Spires, a monument to Francis Scott Key, the National Museum of Civil War Medicine, Monocacy National Battlefield and South Mountain battlefields, and the Schifferstadt Architectural Museum. Adjacent counties Adams County, Pennsylvania (north) Carroll County (east) Franklin County, Pennsylvania (northwest) Montgomery County (south) Washington County (west) Loudoun County, Virginia (southwest) National protected areas Catoctin Mountain Park Chesapeake and Ohio Canal National Historical Park (part) Monocacy National Battlefield Major highways Demographics Frederick County has experienced a rapid increase in population in recent years, including that of minority groups. 2020 census Note: the US Census treats