area codes 227, 240, and 301. These numbers are related to the main zip codes of Maryland.
Maryland consists of the red and blue areas. The red area has area codes 227, 240 and 301.

Area codes 301, 240, and 227 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, Germantown, Bethesda, Rockville, Landover, Silver Spring, and Waldorf.

Area code 301 was the first area code for all of Maryland, from 1947, when the area code system was created, until 1991, when the NPA was reduced in geographic extent. In 1997, it was converted to an overlay numbering plan with the addition of the second area code 240. On June 14, 2023, a third overlay code, 227, was added to provide more central office prefixes for new telephone numbers.

History

Area code 301 was one of the original North American area codes when the American Telephone and Telegraph Company (AT&T) established a new, nationwide telephone numbering plan in 1947. The area code 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.[1] 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.

Ten-digit dialing

By the end of the 1980s, the Washington metropolitan area was running out of assignable prefixes for new central offices. The only unassigned prefixes were unavailable due to the central office code protection that maintained seven-digit dialing in the metro-area. Assignment of these prefixes would require dialing an area code. The three local operating companies of the Chesapeake and Potomac Telephone Company (C&P Telephone, later part of Bell Atlantic and now Verizon) cooperated in ended code protection on October 1, 1990, for entire area and required ten-digit dialing for all local calls between Maryland, the District of Columbia, and Virginia.[2] Area code 202 was no longer usable for suburban points. Local calls within Maryland did not require the area code.[3] Permissive dialing using the old dialing procedures continued from April 1 through October 1, 1990.[4]

410-split

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, it became apparent that terminating central office code protection in the Washington area could not free up sufficient resources north of the Potomac River to stave off the immediate need for a new area code.

In mitigation action, Baltimore and the Eastern Shore were reassigned from area code 301 to area code 410 on November 1, 1991, to form a new numbering plan area.[5][6] The area code split largely followed metropolitan area lines. There were a few exceptions, such as in Howard County, which is often recognized as part of the Baltimore metropolitan area, a small portion of the county remained in 301, while the rest of the county was reassigned to 410.[7]

When an area code is split, the largest city, in this case Baltimore, in the old numbering plan area typically retains the existing area code to minimize expense for changing telephone numbers. In this case, Bell Atlantic spared the large number of federal agencies on the Maryland side of metropolitan Washington from the expense and disruption.

240-overlay

Although the area code split was intended as a long-term solution, within four years 301 was close to exhaustion due to the proliferation of cell phones and pagers, especially in the Washington suburbs. In relief action, area code 240 was introduced on June 1, 1997, to form the state's first overlay.[8] Overlays were a new concept at the time, and met with some resistance due to the requirement for ten-digit dialing.[9] It was decided to create an overlay rather than split the region into two numbering plan areas to avoid assigning a new area code to 1.2 million existing telephone numbers.[10] At the time, it was predicted that it would take until 2008 to exhaust area code 240.[11]

227-overlay

A September 2022 study projected that the 301/240 numbering plan area (NPA) would suffer central office code exhausted between April and June 2023.[12] Area code 227 was already approved as an all-services distributed overlay since January 3, 2001 for the 301/240 NPA.[13][14] The new area code went into service on June 14, 2023, at which time activation of new central office codes could begin, once all assignable central office codes in 240/301 had been exhausted.

Service area

The numbering plan area 301/240/227 include the counties of Allegany, Charles, Garrett, Montgomery, Prince George's, St. Mary's and Washington counties, most of Frederick County,[lower-alpha 1] western Howard County,[lower-alpha 1] and slivers of southwestern Carroll County[lower-alpha 1] and western Anne Arundel County.[lower-alpha 1]

Local calls require ten-digit dialing (area code + number, leading "1" is not required).

Notes

  1. 1 2 3 4 Four counties were split between area code 301 and 410.
    • In Anne Arundel County, Laurel exchanges 210, 317, 490, 497, 498, 596, 604, 725, and 778 and Marlboro exchange 952 remained area code 301. The rest of the county was assigned area code 410.
    • In Carroll County Mount Airy exchange 829 remained area code 301. The rest of the county was assigned area code 410.
    • In Howard County, Mount Airy exchange 829 and Laurel exchanges 210, 317, 490, 497, 598, 604, 725, and 776 remained area code 301. The rest of the county was assigned area code 410.
    • Most of Frederick County remained area code 301. Only Union Bridge exchange 775 and New Windsor exchange 635 were assigned area code 410.[15]

References

  1. ↑ 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.
  2. ↑ "Area Codes Needed to Call Between Md., D.C., Va." The Baltimore Sun. October 1, 1990. p. 2B.
  3. ↑ Jordan, Mary; Quimpo, Margie G. (September 23, 1990). "Territorial Telephones; On Oct. 1, Local Calls Will Get Complicated". The Washington Post. p. 1.
  4. ↑ NANPA Bellcore Information Letter IL-90/04-003
  5. ↑ Muth, Charlie (November 17, 1990). "Shore to Get New Area Code". The Daily Times (Salisbury, Maryland). p. 1, 4.
  6. ↑ Hetrich, Ross (October 25, 1991). "New Area Code 410 Starts Nov. 1 in Half of State". The Baltimore Evening Sun. p. C12.
  7. ↑ "Bellcore Letter IL-90/12-049" (PDF). North American Numbering Plan Administration. Neustar. Retrieved June 21, 2013.
  8. ↑ "Bellcore Letter IL 96/06-009" (PDF). North American Numbering Plan Administration. Neustar. Retrieved 21 June 2013.
  9. ↑ Yates, Jennifer C. (April 22, 1997). "Maryland Gets Read for 10-digit Dialing". Associated Press. The Star-Democrat (Easton, Maryland). p. A1.
  10. ↑ "Ready for 10-digit Stroll?". The Daily Times (Salisbury, Maryland). January 23, 1997. p. 4.
  11. ↑ Pemberton, Mary (May 2, 1997). "10-digit Dialing Comes to Maryland". Associated Press. The Gettysburg Times (Gettysburg, Pennsylvania). p. A3.
  12. ↑ "2022-1 NRUF and NPA Exhaust Analysis" (PDF). North American Numbering Plan Administrator. April 21, 2021. Retrieved July 15, 2021.
  13. ↑ "Planning Letter PL-603: NPA 227 and 240/301 All-Services Overlay (Maryland)" (PDF). NANPA. 2022-09-27. Retrieved 2023-05-27.
  14. ↑ Duffy, Ken (September 28, 2022). "New Area Code Coming to Parts of Maryland". WBAL.
  15. ↑ "New area code for eastern Maryland". The Baltimore Sun. November 1, 1991. p. 1A.
Maryland area codes: 227/240/301, 410/443/667
North: 223/717, 412/724/878, 582/814
West: 202/771, 304/681, 540/826, 571/703 area codes 227/240/301 East: 410/443/667
South: 804, 304/681
District of Columbia area codes: 202/771
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
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