AllAreaCodes.com places 30 Maryland cities including Bethesda, Bowie, Fort Washington and Silver Spring within the 301 area code. Additional major Maryland cities inside the 301 area code include College Park, Fairland, South Laurel and White Oak. The area code also corresponds to Maryland's borders with Washington, D.C.
Additional Maryland cities and communities served by the 301 area code include Hagerstown, Landover, Potomac, Rockville and Waldorf. Most of the phone numbers that the 301 area code serves are mobile phone numbers administered by Verizon. Companies such as Verizon Maryland, New Cingular Wireless, Sprint Spectrum and MCI Worldcom Communications administer mobile and land line numbers using the 301 area code. Some of the counties that the 301 area code serves include Montgomery, Prince George's, Charles and Frederick Counties.
The State of Maryland put the 301 area code into service in 1947; it originally covered the entire state, but was reinstated in 1994 to cover only the western portion of the state. As of 2015, the 240 area code overlays certain portions of the 301 area code and serves many of the same areas. The State of Maryland plans to instate an additional area code, 227, once it exhausts the current available numbers.