Area codes 301 and 240 are telephone area codes in the North American Numbering Plan (NANP) for the western part of the U.S. state of Maryland. The numbering plan area (NPA) comprises Maryland's portion of the Greater Washington, D.C. metro area, portions of southern Maryland, along with rural western Maryland. This includes the communities of Cumberland, Frederick, Hagerstown, Gaithersburg, Potomac, Bethesda, Rockville, Landover, Silver Spring, and Waldorf.
Area code 301 was one of the original area codes when the NANP was established in 1947. It served the entire state of Maryland.
Much of the Washington metropolitan area is part of a local calling area which is centered on the District's area code 202, and also extends into the suburban area in southern Maryland with 301 and Northern Virginia with area code 703. From 1947 to 1990, it was possible to dial any other telephone number in the metro area as a local call with only seven digits, not using an area code, irrespective of the home area code. The entire metro area was also reachable via long-distance services by dialing area code 202, for which purpose AT&T had established cross-referenced operator routing codes for all affected central offices. For example, if 202-574 numbers were in use in the District or 703-574 numbers were in use in Northern Virginia, the corresponding 301-574 numbering block could only be assigned in areas considered a safe distance away from the capital, such as the Eastern Shore of Maryland.
By the end of the 1980s, the Washington metropolitan area was running out of unassigned prefixes for new central offices. The only available prefixes could not be assigned without breaking seven-digit dialing in the region. With this in mind, the three local operating companies of The Chesapeake and Potomac Telephone Company (C&P Telephone, later part of Bell Atlantic and now Verizon) decided to mitigate this situation by ending the code protection scheme as of October 1, 1990, with the result that all local metro area calls between Maryland, the District of Columbia, and Virginia required dialing the area code for calls to another NPA. Area code 202 was no longer useable for suburban points. Local calls within Maryland did not require the area code. Permissive dialing using the old dialing procedures continued from April 1, 1990, through October 1.
Despite the overall growth of the Baltimore���Washington metropolitan area, 301 remained the exclusive area code for Maryland for 44 years, making Maryland one of the largest states with a single area code. By the end of the 1980s, however, it became apparent that breaking seven-digit dialing in the Washington area would not free up enough numbers north of the Potomac River to stave off the immediate need for a new area code.
Baltimore and the Eastern Shore were split off as area code 410 on October 6, 1991. The split largely followed metro area lines. However, part of Howard County, which is recognized as part of the Baltimore area, stayed in 301, while the rest shifted to 410. Normally, when an area code is split, the largest city in the old numbering plan area retains the existing area code—in this case, Baltimore. However, Bell Atlantic wanted to spare the large number of federal agencies on the Maryland side of the metro from the expense and disruption of changing their numbers.
This was intended as a long-term solution, but within four years 301 was close to exhaustion due to the proliferation of cell phones and pagers, especially in the Washington suburbs. To solve this problem, area code 240 was introduced on June 1, 1997, as the state's first overlay area code. Overlays were a new concept at the time, and met with some resistance due to the requirement for ten-digit dialing. For this reason, conventional wisdom would have suggested a split in which the Washington suburbs would have kept 301 while Frederick and points west would have shifted to 240. However, Bell Atlantic wanted to spare residents the burden of having to change their numbers.
Presently, 301/240 is not projected to exhaust until 2026. However, the North American Numbering Plan Administrator has assigned area code 227 as a second overlay for the region as needed. This will have the effect of assigning 23 million numbers to just over two million people.
Portions of the 301/240 territory closest to Washington are still part of a local calling area covering the District and much of Northern Virginia.
The counties served by area codes 301 and 240 include all of Allegany, Charles, Garrett, Montgomery, Prince George's, St. Mary's and Washington counties, most of Frederick County, [a] western Howard County,[a], and slivers of southwestern Carroll County[a] and western Anne Arundel County.[a]
Local calls require ten-digit dialing (area code + number, leading "1" is not required).
- Four counties were split between area code 301 and 410.
- Anne Arundel County was assigned area code 410, except Laurel exchanges 210, 317, 490, 497, 498, 596, 604, 725, and 778 and Marlboro exchange 952 remained area code 301.
- Carroll County was assigned area code 410, except Mount Airy exchange 829 remained area code 301.
- Howard County was assigned area code 410, except Mount Airy exchange 829 and Laurel exchanges 210, 317, 490, 497, 598, 604, 725, and 776 remained area code 301.
- Frederick County remained area code 301, except Union Bridge exchange 775 and New Windsor exchange 635 was assigned 410.
- AT&T Long Lines, Distance Dialing Reference Guide (April 1974) This was implemented via a system of central office code protection, meaning that no central office code in the metro area could exist in more than a single central office.
- Jordan, Mary; Quimpo, Margie G. (September 23, 1990). "Territorial Telephones; On Oct. 1, Local Calls Will Get Complicated". The Washington Post. p. 1.
- NANPA Bellcore Information Letter IL-90/04-003
- "Bellcore Letter IL-90/12-049" (PDF). North American Numbering Plan Administration. Neustar. Retrieved June 21, 2013.
- "Bellcore Letter IL 96/06-009" (PDF). North American Numbering Plan Administration. Neustar. Retrieved 21 June 2013.
- (PDF) https://nationalnanpa.com/reports/2020-2NPAExhaustProjectionsFinal.pdf. Missing or empty
- "New area code for eastern Maryland". The Baltimore Sun. November 1, 1991. p. 1A.
|North: 223/717, 412/724/878, 814|
|West: 202, 304/681, 540, 571/703||area codes 240/301||East: 410/443/667|
|South: 804, 304/681|
|District of Columbia area codes: 202|
|Pennsylvania area codes: 215/267/445, 223/717, 272/570, 412, 484/610, 724, 814/582, 878|
|Virginia area codes: 276, 434, 540, 571/703, 757/948, 804|
|West Virginia area codes: 304/681|