Glen Arm is an unincorporated community in Baltimore County, Maryland, United States. Ravenshurst was listed on the National Register of Historic Places in 1978. Glen Arm was once the home to a Grumman aircraft manufacturing plant. Today, the building serves as the American headquarters of and a wearhouse for Ulla Popken women's clothing. Until 1958, this community was served by the Maryland and Pennsylvania Railroad at milepost 14.5.