North American Numbers Source-cited · ownership disclosed
Area code
301
In service
United States · since 1947

Western/Southern Maryland (D.C. suburbs)

Maryland's original 1947 area code, now serving western and southern Maryland including the Maryland suburbs of Washington, D.C. It is the base code of the 301/240/227 overlay complex.

The essentials Numbering data · NumberResearch · as of 2026-09-18
Place
Western/Southern Maryland (D.C. suburbs)
Type
geographic
Status
in service
In service since
1947
Projected exhaust
2041 Q1

Status, dates and counts are read from NumberResearch (NANPA / CNAC / FCC records). Assignment records show initial assignees, not the carrier serving a number today.

A · Where it is

Where 301 is

Western and southern Maryland: Montgomery, Prince George's, Charles, St. Mary's, Frederick (most), Washington, Allegany, and Garrett counties; western Howard County; and slivers of Carroll and Anne Arundel..

Communities served wholly or partly by 301:

Silver SpringRockvilleBethesdaGaithersburgGermantownFrederickHagerstownCumberlandWaldorf

Overlay complex — 301, 240, and 227 all serve the same territory; ten-digit dialing required.

B · Relationships

How it relates to other codes

The codes 301 was split from, spawned, or shares its area with. A split divides the map and changes some numbers; an overlay shares the same ground and changes none — what's the difference?

Spawned · 1991 410 Baltimore 410 split off from 301 in 1991 for Baltimore and the Eastern Shore.
Overlay · 1997 240 Western/Southern Maryland (overlay) First overlay of 301, in service June 1, 1997 — the state's first overlay.
Overlay · 2023 227 Western/Southern Maryland (overlay) Second overlay of the 301/240 region, in service June 14, 2023.
Related · 1997 443 Baltimore (overlay) Serves the adjacent eastern-Maryland 410 region.
Related · 2012 667 Baltimore (overlay) Serves the adjacent eastern-Maryland 410 region.
What's changing. Base code of the 301/240/227 all-services overlay complex covering western/southern Maryland; ten-digit dialing mandatory.
C · History

How 301 got here

1947
Area code 301 established as one of the original North American area codes, covering all of Maryland.
Source: Wikipedia
1991-10-06
Area code 410 split off for Baltimore and the Eastern Shore; 301 retained the western/southern portion.
Source: Wikipedia
1997-06-01
Area code 240 introduced as the state's first overlay of 301; ten-digit dialing required.
Source: Wikipedia
2023-06-14
Area code 227 added as a third code (second overlay) for the 301/240 region.
Source: Wikipedia
D · Capacity

How full it is

Prefixes assigned
800
Prefixes available
0
Thousands-blocks assigned
2,175

Prefix-assignment counts describe allocation to carriers, not how many individual numbers are in use. Full technical records: NumberResearch ↗.

Compare 301 with another code →
Sources
Wikipedia ↗
Area code 301
NumberResearch.org ↗
Live status, dates, assignment counts and exhaust forecast — data as of 2026-09-18 (CC BY 4.0).

Place, relationships and history above are compiled by North American Numbers from the sources listed and last checked 2026-09-18. A check date is not an expert review — see how this is made. Flag an error.