Silver Spring is an unincorporated community and census-designated place (CDP) in Montgomery County, Maryland, United States. It had a population of 76,716 according to 2013 estimates by the United States Census Bureau, making it the fourth most populous place in Maryland, after Baltimore, Columbia, and Germantown. The urbanized, oldest, and southernmost part of Silver Spring is a major business hub that lies at the north apex of Washington, D.C. As of 2004, the Central Business District (CBD) held 7,254,729 square feet (673,986 m 2) of office space, 5216 dwelling units and 17.6 acres (71,000 m 2) of parkland. The population density of this CBD area of Silver Spring was 15,600 per square mile all within 360 acres (1.5 km 2) and approximately 2.5 square miles (6 km 2) in the CBD/downtown area. The community has recently undergone a significant renaissance, with the addition of major retail, residential, and office developments.Silver Spring takes its name from a mica -flecked spring discovered there in 1840 by Francis Preston Blair, who subsequently bought much of the surrounding land. Acorn Park, tucked away in an area of south Silver Spring away from the main downtown area, is believed to be the site of the original spring. Frederick is a city and the county seat of Frederick County in the U.S. state of Maryland. It is part of the Baltimore–Washington Metropolitan Area. Frederick has been an important crossroads community since it was located in colonial times at the intersection of an important north–south Indian trail, and east–west routes to the Chesapeake Bay both at Baltimore and what became Washington, D.C. and across the Appalachian mountains to the Ohio River watershed. It is a part of the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area, which is part of a greater Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area. The city’s population was 65,239 people at the 2010 United States Census, making it the second-largest incorporated city in Maryland, behind Baltimore.Frederick is home to Frederick Municipal Airport (IATA : FDK), which primarily accommodates general aviation traffic, and to the county’s largest employer U.S. Army’s Fort Detrick bioscience/communications research installation. Mount Rainier / r eɪ ˈ n ɪər / is a city in Prince George’s County, Maryland, United States. The population was 8,080 at the 2010 census. Bordering Washington, D.C., Mount Rainier got its start as a streetcar suburb. (See Streetcars in Washington, D.C.) According to local tradition, surveyors from the Pacific Northwest named the town, giving the streets names such as ” Shasta ” and ” Cascade “. Historic U.S. 1 runs through the center of the town and serves as the main street and central business district.