Area Code 240 History:
Area code 240 was put into service. Area code 240 is an overlay of area code 301.
Counties in Maryland within area code 240 include:
Allegany County, Anne Arundel County, Calvert County, Charles County, Frederick County, Garrett County, Howard County, Montgomery County, Prince Georges County, Saint Marys County, and Washington County.
Major cities or places in Maryland within area code 240 include:
Area codes 240 and 301 serve central and western Maryland including Bethesda, College Park, Frederick, Gaithersburg, Hagerstown, Landover, Rockville, Silver Springs and Weaton-Glenmont in addition to many smaller communities northwest of Washington, D.C.