Area Code 240
Maryland
Area code 240 serves Maryland, primarily Columbia, in the Eastern Time (ET) time zone. It is an overlay area code sharing territory with area code 301.
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 301 (Columbia).
In service since: 01-Jun-1997
Historical Timeline of Area Code 240
Area code 240 was introduced on June 1, 1997, as Maryland's first overlay area code, created to relieve area code 301 which was nearing exhaustion due to rapid cell phone and pager growth in the Washington, D.C. suburbs. The Maryland Public Service Commission chose an overlay over a geographic split to avoid forcing 1.2 million subscribers to change their numbers. Source: Wikipedia
Key milestones:
- 1947: Area code 301 created as one of the original 86 area codes, serving the entire state of Maryland. (Source: NANPA)
- 1990: End of central office code protection required 10-digit dialing for local calls between Maryland, D.C., and Virginia (October 1, 1990). (Source: Wikipedia)
- 1991: Area code 410 split off from 301 on November 1, taking Baltimore and the Eastern Shore. Bell Atlantic kept the western half in 301 to spare federal agencies from number changes. (Source: Wikipedia)
- 1995: Maryland PSC Case No. 8705 approved the overlay plan (Order No. 72274, November 22, 1995), rejecting a geographic split that would have forced approximately 50% of subscribers to change numbers. (Source: Fortnightly Magazine)
- 1996: NANPA Informational Letter IL 96/06-009 notified the industry of NPA 240 as an overlay for 301. Bell Atlantic Maryland reported substantial number growth. 10-digit dialing was permitted from May 1, 1996, and mandatory by May 1, 1997. (Source: NANPA)
- 1997: Area code 240 went into service on June 1 as Maryland's first overlay. Area code 443 followed as an overlay for 410 on July 1. (Source: Wikipedia)
- 2001: Maryland PSC Case No. 8853 (January 3, 2001) approved an all-services distributed overlay as the future relief method for the 240/301 NPA, establishing area code 227 as a reserve overlay. (Source: NANPA)
- 2022: Maryland PSC approved implementation of the 227 overlay on August 3, 2022. NANPA Planning Letter PL-603 was issued September 27, 2022. Network preparation began September 14, 2022. (Source: Maryland PSC)
- 2023: Area code 227 went into service on June 14, 2023 as a third overlay for the 240/301 region, a full 22 years after its initial approval in 2001. (Source: Maryland PSC)
Area code 240's creation reflected a national shift in the mid-1990s toward overlays as the preferred method for number relief. The Maryland PSC's decision in 1995 established a template that avoided the disruption of geographic splits while maintaining full service continuity for existing subscribers.
Unique Facts About Area Code 240
Area code 240 has notable characteristics that distinguishes it within the North American Numbering Plan. Source: Wikipedia, Maryland PSC
- Maryland's first overlay: Area code 240 was introduced on June 1, 1997, as Maryland's first overlay area code. It followed the 1991 split that created area code 410, after which cell phone and pager proliferation quickly exhausted the remaining 301 numbers in the Washington suburbs. (Source: Wikipedia, Maryland PSC)
- 22-year gap between approval and activation: Area code 227 was pre-approved on January 3, 2001 (Maryland PSC Case No. 8853) as a future overlay but was not implemented until June 14, 2023. This 22-year span between regulatory approval and actual deployment is one of the longest such gaps in NANP history. (Source: NANPA)
- Test number 240-999-8378: The original overlay notification (NANPA Informational Letter IL 96/06-009, issued June 21, 1996) included test number 240-999-8378 for the 240 overlay and confirmed that 301 and 240 would share the same boundaries serving the Washington and Hagerstown LATAs. (Source: NANPA)
- Federal agency protection: When the 410 split occurred in 1991, Bell Atlantic deliberately kept the western half of Maryland, including D.C. suburbs housing federal agencies, in area code 301 to spare those agencies from expensive number changes. This decision shaped Maryland's numbering plan for decades and directly led to the creation of 240 as an overlay rather than a second split. (Source: Fortnightly Magazine)
- Overlay chosen to spare 1.2 million subscribers: Verizon estimated that an overlay would be less costly than a geographic split, which would have forced approximately 1.2 million people to change their numbers. The original overlay was predicted to last until 2008; the 227 overlay in 2023 extended the 240/301 region's capacity further. (Source: Wikipedia, Maryland PSC)
Area code 240 now shares its geographic territory with both 301 and 227, covering Montgomery, Prince George's, Frederick, and several other Maryland counties in the greater Washington, D.C. metropolitan area.
FCC Regulatory History
Area code 240 has been shaped by five significant regulatory actions over nearly three decades. The Maryland Public Service Commission's decisions in Case No. 8705 (1995) and Case No. 8853 (2001) established the overlay framework that defines the 240/301 region today. Source: NANPA
| Year | Event | Docket | Regulatory Action & Impact |
|---|---|---|---|
| 1995 | Overlay approval | Case No. 8705 | Maryland PSC approved overlay plan for the 301 NPA (Order No. 72274), rejecting a geographic split that would have forced approximately half of subscribers to change numbers. 10-digit dialing became the standard. (Fortnightly Magazine) |
| 1996 | Industry notification | IL 96/06-009 | NANPA issued Informational Letter notifying the industry of NPA 240 as an overlay for 301. 10-digit dialing permitted from May 1, 1996; mandatory by May 1, 1997. Test number: 240-999-8378. (Source: NANPA) |
| 2001 | Future overlay pre-approval | Case No. 8853 | Maryland PSC approved an all-services distributed overlay as the future relief method for the 240/301 NPA, establishing area code 227 as a reserve overlay to be activated only when number exhaustion was imminent. (Source: NANPA) |
| 2022 | Implementation approval | PL-603 | Maryland PSC approved activation of the 227 overlay on August 3, 2022. NANPA Planning Letter PL-603 issued September 27, 2022. Network preparation began September 14, 2022. (Maryland PSC) |
| 2023 | 227 goes into service | N/A | Area code 227 activated on June 14, 2023 as a third overlay for the 240/301 region. New customers in the Maryland overlay area may now be assigned a 227 number once 240/301 assignable codes are exhausted. (Maryland PSC) |
County Coverage
Population-weighted county share based on aggregated ZCTA population (100% = total mapped population for area code 240).
| 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% |
Call Context
This area code serves the same geographic region as area code 301 in Maryland. It was introduced as an overlay of area code 301, meaning both codes serve the same geographic territory.
Nearby Area Codes
Area codes geographically closest to 240.
Other Area Codes in Maryland
Area codes that also serve Maryland, linked for easy comparison.
Frequently Asked Questions
Common questions about area code 240 and how phone numbering works.
Phone numbers are assigned based on where the number was originally provisioned, not the caller's current location. Mobile phones retain their number when users move, and businesses may use numbers from regions where they don't have a physical presence. VoIP services can also provision numbers from virtually any area code.
Yes, mobile phones can have numbers from any area code in the region they were activated. Wireless carriers assign numbers from available pools regardless of phone type. When users change carriers or move to new areas, they typically keep their original number, which may have a different area code than their current location.
Start by looking up the area code on this site to understand its general geographic region. For the specific number, options include using your carrier's caller ID features or checking public directories. If you suspect fraud, you can report it to the FTC. To file a complaint about robocalls or spoofed numbers, visit the FCC Consumer Complaint Center. You can also register your number with the National Do Not Call Registry to reduce unwanted calls. Keep in mind that caller ID can display any name the caller chooses to set.
When an area's pool of available phone numbers runs low, regulators may introduce an "overlay" area code that covers the same geographic territory as the original. Both codes coexist, and new numbers are assigned from whichever code has availability. This area code shares its region with area code 301, area code 227, area code 301. Learn more in our overlay vs split guide.
While Oakland is a prominent city in this area code's coverage, the code serves the broader surrounding region as well. Area codes are assigned geographically and typically cover multiple cities, towns, and communities beyond any single anchor city.
The estimated total population served by area code 240 is based on aggregated U.S. Census Bureau data for the counties within this area code. The population varies significantly between dense urban codes serving millions and rural codes covering smaller populations. You can find the specific population figure in the demographics section above.