Area Code Atlas

Area code 301 established as Maryland's original area code

Area code 301 was established in 1947 as the original area code for Maryland, covering the entire state when the North American Numbering Plan was created.

NANP - INTRODUCTION OF DIALING PROCEDURE CHANGES IN THE 202 AND PORTIONS OF THE 301 AND 703 NUMBERING PLAN AREA (NPAS)

Ten-digit dialing required in Washington metropolitan area

On October 1, 1990, central office code protection ended in the Washington metropolitan area, and ten-digit dialing became mandatory for local calls between Maryland, the District of Columbia, and Virginia. The Washington metropolitan dialing-plan change affecting portions of 301 became mandatory on this date, ending seven-digit dialing for adjacent-NPA local calls within the metropolitan area.

Mandatory 10-digit dialing implemented in the Washington, D.C. metro area

On October 1, 1990, mandatory 10-digit dialing was implemented for all local calls between Maryland (301), the District of Columbia (202), and Northern Virginia (703) in the Washington Metropolitan Exchange Area. This change ended the previous system of seven-digit local dialing across the metro area. New dialing procedures became mandatory, with ten-digit dialing required for foreign-NPA local calls and 1+ten-digit dialing for direct-dialed toll calls.

Split of NPA 301 and introduction of NPA 410 announced

Bellcore issued industry notification that Maryland's 301 numbering plan area would be split and that the new 410 area code would be introduced for the eastern part of the state. The notice established an effective split date of October 6, 1991 and described a permissive dialing period extending until November 1, 1992. It also documented the post-split geography, with 301 continuing to serve western and Washington-suburban Maryland.

NPA 410 split from 301 in Maryland

Area code 410 was created on October 5, 1991, as a split from 301 to address number exhaustion in Maryland. The new code covered most of Maryland from the Baltimore area eastward, while 301 continued to serve the Washington metropolitan area.

NPA 410 split from 301

Area code 410 officially entered service on October 6, 1991, following a split from 301. The new code covered the Baltimore metropolitan area and Maryland's Eastern Shore, while 301 continued to serve western and southern Maryland.

NPA 410 split from 301 for Baltimore and Eastern Shore

On November 1, 1991, area code 410 was created as a geographic split from area code 301. The new code served Baltimore, the Eastern Shore, and parts of central Maryland, while 301 continued to serve western Maryland and the Washington, D.C. suburbs.

Ten-digit dialing required for inter-NPA calls in Maryland

Effective November 1, 1991, ten-digit dialing became mandatory for calls between different area codes within Maryland, following the introduction of area code 410 and the split from 301.

Permissive ten-digit local dialing begins in Maryland for 240 overlay preparation

In preparation for Maryland's overlay implementation, permissive ten-digit local dialing began on May 1, 1996. During this stage, callers within Maryland could begin using area code plus number for local calls while networks and customer equipment were adjusted. The permissive phase was part of the transition needed before mandatory ten-digit dialing and overlay activation.

Overlay relief using NPA 240 for 301 is announced

Bellcore issued formal notice that NPA 240 had been assigned to relieve 301 in western Maryland under a general-purpose overlay plan approved by the Maryland Public Service Commission. The notice explained that 301 and 240 would share the same geographic boundaries and that existing 301 telephone numbers would not change. It also set out the associated ten-digit dialing transition schedule needed for the overlay's implementation.

Correction to 301 NPA (Maryland) Relief Plan Contact Information

NPA 240 overlays 301 in Maryland

Area code 240 was introduced in 1997 as an overlay for the 301 area in Maryland, providing additional numbering resources for the region.

Mandatory ten-digit local dialing begins in Maryland for overlay implementation

Mandatory ten-digit local dialing within Maryland began on May 1, 1997 as part of the overlay transition. Bellcore stated that conversion of central offices for mandatory ten-digit dialing would begin on that date and continue through the overlay's in-service date. This dialing change was necessary because overlay relief allows multiple area codes to share the same territory.

Area code 240 overlays 301 in Maryland

On June 1, 1997, area code 240 was introduced as an overlay for area code 301 in Maryland, covering parts of Montgomery and Prince George's counties, and was Maryland's first overlay. This change was implemented to address number exhaustion in the Washington, D.C. metropolitan area. Under the overlay plan, 240 and 301 served the same geographic area, allowing existing 301 subscribers to keep their numbers while new numbering resources could be assigned from 240.

Mandatory 10-digit dialing for 301/240 overlay complex

Mandatory 10-digit dialing began in June 1997 for all calls within the 301/240 overlay region in western Maryland. This requirement accompanied the introduction of the 240 overlay to ensure proper call routing.

NPA 227 approved as future overlay relief for 240/301

According to NANPA Planning Letter PL-603, the Maryland Public Service Commission approved an all-services distributed overlay as the relief method for the 240/301 numbering plan area on January 3, 2001 in Case No. 8853. This approval established 227 as the designated future relief code for the area. The decision did not immediately place 227 in service, but it set the long-range relief method for the NPA complex.

Implementation of the 227 overlay for 240/301 is approved

NANPA reported that on August 3, 2022 the Maryland Public Service Commission issued a letter approving implementation of the previously selected 227 overlay for the 240/301 numbering plan area. This action moved the long-approved relief method into active implementation. It preceded NANPA's formal planning letter and the customer-education and network-preparation schedule.

NANPA issues planning letter for NPA 227 overlay implementation

NANPA issued Planning Letter PL-603 on September 27, 2022 for the 227 all-services overlay on the 240/301 area. The letter set out the implementation schedule, including customer education, network preparation, code ordering, and testing milestones. It also reiterated that 227 codes would be available only after assignable codes in 240 and 301 were exhausted.

Approval of 227 overlay for 301/240

On September 27, 2022, the Maryland Public Service Commission approved the implementation of area code 227 as an all-services distributed overlay for the 301/240 numbering plan area. The overlay was planned to address the projected exhaustion of available numbers.

Area code 227 overlays 240/301 in Maryland

On June 14, 2023, area code 227 was introduced as an overlay for the Maryland 240/301 region, covering Allegany, Charles, Garrett, Montgomery, Prince George's, St. Mary's, and Washington counties, as well as parts of Frederick, Howard, Carroll, and Anne Arundel counties. This addition provided new central office prefixes to meet demand after the projected exhaustion of available numbers. NANPA designated that date as the earliest activation date for new 227 central office codes, with assignment allowed only after all assignable codes in 240 and 301 had been exhausted. From that point forward, 227 joined 240 and 301 as coextensive area codes serving the same Maryland territory.