Area Code 301
Maryland
Area code 301 serves Maryland, primarily Columbia, in the Eastern Time (ET) time zone. It has served the region since 01-Jan-1947.
Overlay Area Codes
This area code is part of an overlay region, meaning the same geographic area is served by multiple area codes. Overlay codes were introduced to meet growing demand for phone numbers without requiring existing customers to change their numbers.
This area code shares its geographic region with: area code 227 (Columbia), area code 240 (Columbia).
In service since: 01-Jan-1947
Area Code Splits
Parts of this area code’s original geographic region were later assigned new area codes through splits. When a split occurs, some customers in the original area code region are assigned the new area code.
Split into: area code 410 (Baltimore).
Demographics & Economics
Demographic Data Unavailable for Area Code 301
County-level demographic data is not available for this area code because NPA boundary polygons are not publicly distributed by NANPA. We use geographic boundary data from the Colorado Open Data Portal to map area codes to counties, which currently covers 194 of 376 geographic area codes.
Demographic statistics (population, income, education, poverty) require county-level aggregations from Census ACS data. Without a county mapping, these aggregations cannot be computed. We are actively seeking additional data sources to improve coverage.
Statistics are population-weighted aggregations from Census ACS 5-year estimates where county boundary data is available.See Sources for details.
Time Zone
- Eastern Time (ET)
NANPA Relief Status
According to the latest NANPA analysis (July 2026), this area code is not currently listed as exhausting within the next 36 months. No relief planning is in progress for this NPA.
Source: NANPA NPA Relief Planning Reports · See all relief planning statuses
Current Time
Prefix Utilization
Geographic Coverage
State
MD
Major Cities
- Columbia
- Germantown
- Waldorf
- Silver Spring
- Frederick
- Gaithersburg
- Bethesda
- Rockville
- Bowie
- Aspen Hill
- Wheaton
- North Bethesda
- Potomac
- Hagerstown
- Clinton
- Olney
- Chillum
- College Park
- Montgomery Village
- Crofton
- Laurel
- Clarksburg
- South Laurel
- Fairland
and 301 more cities
Historical Timeline of Area Code 301
Area code 301 was created on January 1, 1947 as one of the original 86 area codes in the North American Numbering Plan, covering the entire state of Maryland. It has undergone three major changes: a 1991 split creating area code 410 for Baltimore and the Eastern Shore, a 1997 overlay adding area code 240 as Maryland's first overlay, and a 2023 overlay adding area code 227, bringing the total to three area codes sharing the same western Maryland and DC suburban territory. Source: Wikipedia
Key milestones:
- 1947: Created as one of the original 86 area codes covering all of Maryland (NANPA / AT&T Bell System)
- October 6, 1991: 410 split removed Baltimore and Eastern Shore. 301 retained DC suburbs and western Maryland. Permissive dialing extended until November 1, 1992 (NANPA IL 90-12-049)
- June 1, 1997: 240 overlay added as Maryland's first overlay area code. Mandatory 10-digit dialing implemented (NANPA IL 96-06-009)
- January 3, 2001: Maryland PSC Case No. 8853 approved all-services distributed overlay framework for 240/301, reserving 227 for future use
- August 3, 2022: Maryland PSC approved implementation of 227 overlay after NANPA petition. Estimated 240/301 exhaust in Q2 2023 (Maryland PSC)
- June 14, 2023: 227 area code went into service as second overlay for the 301/240 region (Maryland PSC)
The 301 area code has served the Washington DC metropolitan suburbs and western Maryland for nearly 80 years. The 1991 split was driven by exhaust pressure from the growing Baltimore region, while the 1997 and 2023 overlays addressed continued growth in the DC suburban corridor.
Regulatory History
Area code 301 has been the subject of five major regulatory actions since 1990, spanning NANPA planning letters and Maryland Public Service Commission decisions. These actions shaped the numbering plan for Maryland's western and suburban regions. Source: Wikipedia
| Year | Event | Docket | Regulatory Action & Impact |
|---|---|---|---|
| 1990 | 410 Split | NANPA IL 90-12-049 | Split of 301 NPA created area code 410 for Baltimore and Eastern Shore, effective October 6, 1991. Permissive dialing extended until November 1, 1992 |
| 1996 | 240 Overlay | NANPA IL 96-06-009 | Overlay of 301 NPA introduced area code 240 as general purpose overlay. Activated June 1, 1997. Mandatory 10-digit dialing from May 1, 1997 |
| 2001 | All-Services Overlay Framework | Maryland PSC Case No. 8853 | Maryland PSC approved all-services distributed overlay as relief method for 240/301 NPA. Established framework reserving area code 227 for future use |
| 2022 | 227 Overlay Approval | Maryland PSC | Approved NANPA petition to implement 227 area code overlay for 240/301 region. Estimated 240/301 exhaust in Q2 2023 (Maryland PSC) |
| 2022 | 227 Implementation Notice | NANPA PL-603 | Notified industry of 227 overlay implementation. Network preparation began September 14, 2022. In-service date June 14, 2023. 227 CO codes available only after 240/301 exhaustion |
County Coverage
Population-weighted county share based on aggregated ZCTA population (100% = total mapped population for area code 301).
| County | Population | Share |
|---|---|---|
| Montgomery, MD | 1,168,712 | 34.4% |
| Prince George's, MD | 1,082,938 | 31.9% |
| Frederick, MD | 336,420 | 9.9% |
| Charles, MD | 220,971 | 6.5% |
| Washington, MD | 173,549 | 5.1% |
| Howard, MD | 127,684 | 3.8% |
| St. Mary's, MD | 118,020 | 3.5% |
| Allegany, MD | 69,925 | 2.1% |
| Garrett, MD | 46,232 | 1.4% |
| Carroll, MD | 35,637 | 1.0% |
| Anne Arundel, MD | 7,512 | 0.2% |
| Calvert, MD | 7,512 | 0.2% |
Area Code 301 Family Tree
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All Descendants
Area code 301 was originally assigned in 01-Jan-1947 to serve MD. Over the years, it has generated 5 descendant area codes through a combination of geographic splits and overlays as demand for telephone numbers grew.
Call Context
This area code covers a geographic region across MD, including Columbia and surrounding communities.
Nearby Area Codes
Area codes geographically closest to 301.
Other Area Codes in Maryland
Area codes that also serve Maryland, linked for easy comparison.