Green Valley is an unincorporated area and census-designated place (CDP) in southern Frederick County, Maryland, United States. The population was 12,643 at the 2020 census. The area was listed as a census-designated place in 2000 but not listed as part of any CDP at the 2010 census. It was re-designated a census-designated place for the 2020 census.
Geography
The Green Valley area is located in southeastern Frederick County at (39.341801, −77.240437), bordered to the south and east by Montgomery County. The northern edge of the CDP extends from Mount Airy in the northeast to New Market in the northwest. The unincorporated community of Monrovia is located just to the west.
According to the United States Census Bureau, the Green Valley CDP had a total area of , all land.