Maryland’s 240 area code pioneered the overlay: a second code laid directly over 301’s territory, from the Washington, DC suburbs through Southern Maryland to the mountain panhandle in the far west. It has shared that ground with 301 since June 1, 1997, and nobody’s number changed the day it arrived. That was the whole point.
Most area codes are defined by their borders. 240 is defined by what it sits on top of — and by the fact that the model it tested became how American numbering relief gets done.
Two codes, one stretch of Maryland
240 and 301 are fully interchangeable across the same footprint. The Maryland Public Service Commission draws it as Allegany, Charles, Garrett, Montgomery, Prince George’s, St. Mary’s, and Washington counties, plus parts of Frederick, Howard, Carroll, and Anne Arundel. NANPA’s planning letter for the region names Silver Spring, Bethesda, Wheaton, Potomac, Gaithersburg, Germantown, Bowie, Waldorf, Frederick, Hagerstown, and Cumberland.
The sweep is wide: the same pair of codes serves the Beltway science corridor — NIH in Bethesda, NIST in Gaithersburg — the I-270 commuter belt, the tobacco-barn flatlands of St. Mary’s County, and Appalachian ridge towns two hours from the District. Baltimore and the Eastern Shore are a different numbering world: 410 and its overlays.
What 240 on a caller ID really says
One inference and one warning. The inference: a 240 number cannot predate mid-1997, so the code skews toward newer lines — mobiles, VoIP services, younger businesses — while a 301 can be a suburban landline that has answered the same digits for generations.
The warning: neither code proves location. Ported numbers keep their digits in a new city, VoIP answers wherever there is bandwidth, and a spoofer can dress a robocall in local digits, up to a neighbor-spoofed 240 or 301. A genuine county office, school, or Bethesda practice will still answer when you redial its published line; an impostor won’t.
When 301 had Maryland to itself
301 was one of the original area codes drawn up in 1947 and covered every telephone in the state for 44 years. Then growth forced a classic split: on October 6, 1991, Baltimore and the eastern half of Maryland moved to the new 410 area code, while 301 kept the Washington suburbs, Southern Maryland, and the west.
The relief bought less time than planned. The 1990s stacked second lines, fax machines, modems, and the first cellphones onto the DC suburbs, and 301 was burning through prefixes again within a few years. Splitting a second time meant another mass renumbering for one of the country’s busiest phone regions.
June 1, 1997: the second code switches on
Maryland’s regulators reached for the tool almost nobody had used: a new code over the same map. 240, assigned by the numbering administrator on June 21, 1996, entered service on June 1, 1997 — the same morning 443 lit up over Baltimore’s 410 territory. Existing customers kept every digit; new lines drew from the second pool.
Only one overlay existed anywhere in the North American Numbering Plan before that day: New York’s 917, in service since 1992 and aimed at cellphones and pagers. Maryland’s pair were the first covering every kind of service, landlines included — the moment the overlay went from experiment to standard practice. Our what-is-an-area-code explainer weighs the split-versus-overlay trade in detail.
Ten digits, twenty-nine years and counting
An overlay has one unavoidable cost: with two codes on the same ground, seven digits no longer identify a line, so every local call carries all ten. The 240/301 region crossed that bridge at the 1997 launch, decades before most of the country followed.
The payoff arrived in 2021. As 988 rolled out as the national crisis line, NANPA Planning Letter PL-556 named the 82 area codes still permitting seven-digit dialing that now had to convert. Not one Maryland code appears on that list. The conversion the rest of the country scrambled through, this region had finished 24 years early.
227: a third code, 22 years on layaway
The overlay pioneer eventually needed an overlay of its own. The Maryland PSC approved a distributed overlay as the next round of 240/301 relief on January 3, 2001, in Case No. 8853, and NANPA assigned 227 to the job that same month. Then the emergency receded: conservation measures and fading landline demand stretched the pool, and 227 sat on the shelf for two decades.
The clock ran out in 2022: the Commission approved implementation on August 3, NANPA Planning Letter PL-603 followed on September 27, and 227 entered service on June 14, 2023. One rule keeps it scarce — a 227 prefix is assigned only after every assignable 240 and 301 prefix is gone. Our NPA-NXX guide covers how prefix inventory works.
Putting the 240/301 map to work
In the DC orbit, the area code is tribal shorthand: 301 and 240 read as the Maryland side of the region, distinct from the District’s code and Northern Virginia’s. For contractors, medical practices, and government-adjacent firms selling into Montgomery, Prince George’s, or Frederick counties, a local display earns pickups an outside number never will; we lay out the answer-rate data in our breakdown of local presence dialing.
SIPNEX sources 240/301 DIDs by rate-center inventory and brings them to your phone system on SIP trunking, signing outbound traffic at the A level under our company-held STIR/SHAKEN certificate — verification a spoofed Maryland number cannot carry.
Frequently asked questions
Which Maryland counties does the 240 area code cover?
240 shares its footprint with 301: Allegany, Charles, Garrett, Montgomery, Prince George’s, St. Mary’s, and Washington counties, plus parts of Frederick, Howard, Carroll, and Anne Arundel, per the Maryland PSC. Major communities include Silver Spring, Bethesda, Rockville, Gaithersburg, Frederick, Hagerstown, Waldorf, and Cumberland. Baltimore and the Eastern Shore use 410, 443, and 667 instead.
Is a 240 number in a different place than a 301 number?
No. 240 is an overlay: both codes cover identical territory and cost the same to call. The difference is vintage — 301 has been issued since 1947, 240 only since June 1, 1997. Since June 14, 2023 a third code, 227, shares the map, its prefixes opening only as the older pools run dry.
Why did Maryland overlay 240 instead of splitting 301 again?
Because the 1991 split that created 410 had already forced half the state to change numbers, and regulators didn’t want a repeat. Overlaying 240 kept every existing 301 number intact and simply opened a parallel pool for new lines, at the price of ten-digit local dialing. Maryland applied the model to all services first, and it became the national default for relief.
Has the 240 area code always required ten-digit dialing?
Yes — from its first day of service on June 1, 1997, because two codes on the same ground make seven digits ambiguous. That head start left the region untouched by the 2021 conversion for the 988 crisis line: NANPA Planning Letter PL-556 lists 82 area codes forced to ten digits, and none are in Maryland.
Can I still get a new 240 phone number?
Yes, where rate-center inventory holds 240 or 301 prefixes. Under NANPA’s PL-603 plan, new 227 prefixes are assigned only once every assignable 240 and 301 prefix is exhausted, so fresh Maryland numbers keep drawing on the two older pools wherever that inventory lasts. Availability varies by rate center, which is how carriers provision local numbers.
Behind every Maryland number SIPNEX issues sits an FCC carrier license, rate-center DID inventory nationwide, RespOrg toll-free service, and volume SIP trunking, with outbound calls signed at the A level on our own STIR/SHAKEN certificate. Call us at (833) 665-2220, email the team, or look over rates.
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