240 Area Code Guide: Maryland's DC Suburbs

The 240 area code is a geographic North American Numbering Plan (NANP) overlay code serving western and southern Maryland. It operates across the same footprint as area codes 301 and 227 — all three codes reach the same counties, agencies, and businesses throughout the region.

The 240/301/227 numbering plan area spans western, central, and southern Maryland, covering a broad crescent of suburbs and rural communities surrounding Washington, D.C.:

Businesses that want to activate service right away can start with local phone numbers.

Western Maryland's area code history reflects the explosive growth of Washington, D.C.'s suburban ring over eight decades.

1947 — Area Code 301: At the founding of the North American Numbering Plan, all of Maryland is assigned area code 301 — covering everything from Baltimore to the western mountains in a single numbering plan area.

November 1, 1991 — Area Code 410 splits off: Baltimore and eastern Maryland's rapid growth depletes the 301 number pool. Area code 410 is carved out to cover Baltimore and the eastern counties.

June 1, 1997 — Area Code 240 launches: The proliferation of mobile phones and pagers in the densely populated DC suburbs pushes 301 toward exhaustion. Maryland introduces its first overlay: area code 240 is assigned to the same territory as 301, and mandatory 10-digit dialing takes effect.

June 14, 2023 — Area Code 227 launches: Area code 227 had been approved for the 301/240 region as far back as January 3, 2001 — but was not implemented for 22 years, as alternate number conservation methods bought time. When 227 finally went live in June 2023, the western Maryland territory became a three-code overlay.

For a detailed numbering history, see Wikipedia's overview of the 240 area code.

No county in Maryland — and arguably no county in the United States — concentrates more federal science capacity per square mile than Montgomery County.

The county's Gross Domestic Product exceeds $117 billion, representing a full 25% of Maryland's total state economy. That output is anchored by an extraordinary combination of federal institutions and the private sector they have seeded.

Federal Science Agencies. Montgomery County hosts 18 federal agencies and 36 federal labs including the Food and Drug Administration (FDA) in White Oak, the National Institutes of Health (NIH) on its 300-acre Bethesda campus, the National Institute of Standards and Technology (NIST) in Gaithersburg, and the National Cybersecurity Center of Excellence (NCCoE). The county employs 11,755 HHS employees — 33% of Maryland's total HHS workforce — generating $1.7 billion in wages.

The Biopharma Cluster. Seeded by decades of NIH and FDA proximity, Montgomery County has grown into the third-largest biopharma hub in the United States, with more than 350 life science companies specializing in gene therapies, cell therapies, vaccines, and pharmaceutical manufacturing. Recent investments include:

Directly adjacent to Montgomery County and sharing the same 240/301 area code, Prince George's County represents the defense operations and federal administrative anchor of the Washington suburban corridor.

The county generates $34.5 billion in annual economic output and hosts a constellation of federal facilities:

The county is also home to the University of Maryland (College Park) — a flagship research university with 40,000+ students — and IonQ, which operates a leading quantum computing facility in the county.

Beyond Montgomery and Prince George's Counties, the 240/301/227 footprint extends across a diverse arc of Maryland communities.

Frederick County has emerged as one of the fastest-growing counties in the state, with its county seat of Frederick serving as a logistics and manufacturing hub midway between Baltimore and Washington. The county's proximity to both metro areas — and lower land costs than Montgomery County — has attracted significant warehouse, distribution, and light manufacturing investment along the I-270 corridor.

Charles County and Southern Maryland anchor a distinct economy around Naval Air Station Patuxent River (in St. Mary's County), the Navy's primary aircraft test and evaluation facility.

NAS Patuxent River employs approximately 22,000 military and civilian personnel, generating billions in defense-related economic activity along the southern Maryland corridor.

Western Maryland — Allegany, Garrett, and Washington Counties — adds a resource and tourism economy, including Cumberland's manufacturing heritage, Hagerstown's logistics position on I-81, and Deep Creek Lake's outdoor recreation economy. Companies serving these diverse markets rely on an omnichannel communication platform to reach clients consistently across every channel.

For companies targeting the federal government, defense contractors, life science institutions, or any commercial market in Maryland's DC suburbs, a 240 number delivers access and credibility that out-of-state or unfamiliar prefixes cannot match.

Federal Procurement Access. Montgomery County's 18 federal agencies and Prince George's County's Joint Base Andrews, NASA Goddard, and Census Bureau headquarters collectively represent billions of dollars in annual vendor contracts. Federal procurement officers and contracting teams apply a local-presence filter — a Maryland number signals genuine proximity and commitment to the DC market.

Biopharma and Life Science Vendor Market. The 350+ life science companies clustered in Rockville, Gaithersburg, and the I-270 biotech corridor form one of the most active vendor markets in the country. CROs, lab equipment suppliers, regulatory consultants, and clinical data firms all compete for relationships within this cluster.

Twenty-Six Years of Established Identity. The 240 area code launched in 1997 and operated alongside only 301 for 26 years before 227 arrived in 2023. In the federal contracting and biotech procurement worlds — where vendor relationships are built over years and reference checks go deep — that longevity matters.

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