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. Rockville is a city located in the central region of Montgomery County, Maryland. It is the county seat and is a major incorporated city of Montgomery County and forms part of the Baltimore–Washington metropolitan area. The 2010 census tabulated Rockville’s population at 61,209, making it the third largest incorporated city in Maryland, behind Baltimore and Frederick. Rockville is the largest incorporated city in Montgomery County, Maryland, although the nearby census-designated place of Germantown is more populous. Rockville, along with neighboring Gaithersburg and Bethesda, is at the core of the Interstate 270 Technology Corridor which is home to numerous software and biotechnology companies as well as several federal government institutions. The city also has several upscale regional shopping centers and is one of the major retail hubs in Montgomery County. Hyattsville is a city in Prince George’s County, Maryland, and also a close, urban suburb of Washington, D.C. The population was 17,557 at the 2010 United States Census.