Mount Airy is a city located in Carroll and Frederick counties in the U.S. state of Maryland. It is part of both the Washington Metropolitan Area and Baltimore Metropolitan Area. As of the 2010 census it had a population of 9,288.
Outside of the city limits, the surrounding community is colloquially referred to as Mount Airy or the "Four-County Area" by locals. The "Four-County Area" derives its name from the fact that the community encompasses portions of Frederick, Carroll, Montgomery, and Howard counties.