North American Numbers Source-cited · ownership disclosed
Area code
240
In service
United States · since 1997

Western/Southern Maryland (overlay)

An overlay of 301 covering western and southern Maryland — the Maryland suburbs of Washington, D.C. Introduced June 1, 1997, it was the first overlay area code in Maryland.

The essentials Numbering data · NumberResearch · as of 2026-09-18
Place
Western/Southern Maryland (overlay)
Type
geographic
Status
in service
In service since
1997
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 240 is

Western and southern Maryland: same footprint as 301 — Montgomery, Prince George's, Charles, St. Mary's, Frederick, Washington, Allegany, and Garrett counties, plus parts of Howard, Carroll, and Anne Arundel..

Communities served wholly or partly by 240:

Silver SpringRockvilleBethesdaGaithersburgGermantownFrederickHagerstownCumberlandWaldorf

Same geography as 301 and 227 — an overlay, not a distinct area.

B · Relationships

How it relates to other codes

The codes 240 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?

Overlay · 1997 301 Western/Southern Maryland (D.C. suburbs) 240 overlays 301; both share the western-Maryland footprint.
Overlay · 2023 227 Western/Southern Maryland (overlay) Third code added to the same 301/240 region.
Related · 1991 410 Baltimore 301 (240's base) originally spawned 410 for eastern Maryland.
What's changing. Overlay of 301 within the 301/240/227 complex; ten-digit dialing mandatory.
C · History

How 240 got here

1997-06-01
Area code 240 entered service as Maryland's first overlay, over the 301 region; ten-digit dialing required.
Source: Wikipedia
2023-06-14
Area code 227 added as a further overlay of the shared 301/240 region.
Source: Wikipedia
D · Capacity

How full it is

Prefixes assigned
800
Prefixes available
0
Thousands-blocks assigned
5,929

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

Compare 240 with another code →
Sources
Wikipedia ↗
Area code 240
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.