Silver Spring is a census-designated place (CDP) in southeastern Montgomery County, Maryland, United States, near Washington, D.C. Although officially unincorporated, in practice it is an edge city, with a population of 81,015 at the 2020 census, making it the fifth-most populous place in Maryland after Baltimore, Columbia, Germantown, and Waldorf. 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, south of downtown, is believed to be the site of the original spring.