Mount Aetna is a census-designated place (CDP) in Washington County, Maryland, United States.

According to the United States Census Bureau, the CDP has a total area of 3.9 square miles (10 km2), all land.

The community is situated at the western base of South Mountain at elevations between 500 and 700 feet; the landscape here is principally underlain by the Tomstown Dolomite, and the neighboring area is home to at least four known solutional caves, one of which—Mount Aetna Cave—was open briefly for commercial tours in the 1930s.

There was once a small convenience market, but now the only food store in the community is located on the academy grounds.

This store sells books, vegetarian meat substitutes, and Big Texas rolls, which are loved by the chunky students.