631 Area Code: A Guide to Huntington, Babylon, and Suffolk County, New York

Quick answer: Area code 631 is the telephone prefix for Suffolk County, New York — the eastern half of Long Island, stretching from Huntington and Babylon in the west through Smithtown, Islip, and Brookhaven in the center, to the Hamptons, Riverhead, and the North Fork in the east. It covers every incorporated town and village in Suffolk County in the Eastern Time Zone and shares the county with overlay area code 934, with ten-digit dialing mandatory for all local calls since June 2016.

What territory does area code 631 cover?

Area code 631 is the primary telephone prefix for Suffolk County — the easternmost and largest county on Long Island, New York. It covers a 912-square-mile territory that runs the full length of the Island's eastern portion, from the dense suburban communities along the Long Island Expressway corridor in the west to the barrier beaches, wine country, and oceanfront villages of the East End.

Crucially, 631 covers Suffolk County only. The neighboring county to the west — Nassau County, which includes communities like Hempstead, Garden City, and Long Beach — uses area code 516. The county line between Nassau and Suffolk is the de facto boundary between the two codes, and callers crossing it must use the full ten-digit format in both directions.

The 624 area code, which similarly covers a single county-level overlay territory in upstate New York, offers a useful in-state parallel: like 631, it was born of subscriber growth in a distinct regional community with a strong local identity that no area code reassignment could change.

Towns, villages, and communities across the 631 footprint

Suffolk County's ten towns form the geographic backbone of the 631 territory — a diverse landscape of suburban corridors, preserved farmland, national seashores, and internationally recognized resort communities that make it one of the most economically varied county-level area code footprints in the northeastern United States.

Major towns and communities in the 631 service area:

• Huntington — Suffolk County's northernmost western town along the Long Island Sound, anchoring a densely populated suburban and commercial corridor with a nationally recognized downtown, a significant arts and entertainment district, and major healthcare institutions including Huntington Hospital and Northwell Health facilities
• Babylon — South Shore town along the Great South Bay, home of Fire Island's western access communities including Amityville, Copiague, Lindenhurst, and West Babylon, serving as a commuter hub for the Long Island Rail Road's Babylon Branch
• Islip — Central Suffolk town encompassing Brentwood, Central Islip, Bay Shore, Oakdale, and the eastern bay communities; home of Long Island MacArthur Airport and the Dowling College corridor; Brentwood and Central Islip are among the county's most populous communities
• Smithtown — North Shore town anchoring a residential, commercial, and healthcare corridor centered on Smithtown, Commack, Kings Park, and Hauppauge; Commack is one of Suffolk's most affluent suburban communities
• Brookhaven — Suffolk County's largest town by area, spanning the Island's full width from Sound to sea and encompassing Patchogue, Coram, Medford, Centereach, Ronkonkoma, Port Jefferson, and the village of Bellport; home of Brookhaven National Laboratory
• Southampton — East End town anchoring the Hamptons corridor from Hampton Bays through Southampton Village to Water Mill and Bridgehampton, one of the wealthiest and most internationally recognized resort communities in the United States
• East Hampton — The easternmost Hamptons town, encompassing East Hampton Village, Montauk, Amagansett, and Springs; Montauk anchors a year-round fishing, surfing, and resort economy at the tip of the South Fork
• Riverhead — Suffolk County seat and the geographic center of the Island's East End, a growing retail and distribution hub home of Tanger Outlets Riverhead and the regional government complex
• Southold — North Fork town anchoring Long Island's wine country, home of more than 60 wineries and vineyards along the Route 48 and Main Road corridors between Cutchogue and Greenport
• Shelter Island — Island town accessible only by ferry, a small-community retreat positioned between the North and South Forks at the head of Peconic Bay

Selected communities by area:

The entire 631 territory observes Eastern Time (UTC−5 in winter, UTC−4 during DST) — the same zone as New York City, Boston, and Washington, D.C. Callers from the Central Time Zone should account for the one-hour difference when scheduling calls with Suffolk County contacts.

How Long Island went from one area code to two

Long Island's telephone history began in 1951, when area code 516 was assigned to cover both Nassau and Suffolk counties as a single prefixed territory — one of the original reorganizations of the 1947 North American Numbering Plan that created geographically smaller codes to handle expanding metropolitan subscriber bases.

For nearly five decades, 516 served all of Long Island. Through the postwar suburban boom of the 1950s and 1960s, the growth of the defense and aerospace industry anchored by Grumman Corporation and Fairchild Republic in the 1970s and 1980s, and the early cellular expansion of the 1990s, a single code absorbed the entire Long Island subscriber base. By the late 1990s, that capacity was no longer sufficient.

The surge in cellular subscriptions through the mid-1990s consumed 516's remaining central office prefixes faster than any previous technology wave. Rather than add an overlay to both counties, regulators chose a geographic split: Nassau County retained 516, while Suffolk County received the new code 631, effective November 1, 1999. A permissive dialing period allowed both the old 516 digits and the new 631 prefix to reach Suffolk subscribers through April 1, 2000, after which 631 became mandatory for all Suffolk lines.

Suffolk's continued growth — particularly in mobile subscribers, VoIP services, and residential expansion into the county's eastern towns — eventually brought 631 itself toward exhaustion. The New York State Department of Public Service, which administers telecommunications regulation for the state alongside NANPA, approved area code 934 as an all-services overlay for 631.

Mandatory ten-digit dialing across the entire 631 territory began on June 18, 2016, and 934 went into service on July 16, 2016 — giving Suffolk County its second prefix without changing a single existing number.

Key milestones:

• 1951 — 516 assigned to all of Long Island (Nassau and Suffolk counties)
• November 1, 1999 — 631 split from 516; Nassau retains 516, Suffolk receives 631
• April 1, 2000 — Permissive dialing ends; 631 mandatory for all Suffolk lines
• June 18, 2016 — Ten-digit dialing becomes mandatory across the 631/934 territory
• July 16, 2016 — 934 activated as all-services overlay for Suffolk County

Making and receiving 631 calls

Because 631 and 934 share the same Suffolk County territory as overlays, ten-digit dialing is mandatory for all local calls — whether between two 631 numbers, from 631 to 934, or from 934 to 631. Callers anywhere on Long Island must dial all ten digits regardless of carrier, device type, or geographic proximity.

Time zone tip: All 631 communities observe Eastern Time — the same zone as New York City, Philadelphia, and Miami. Suffolk County runs one hour ahead of Chicago and three hours ahead of the Pacific Coast. West Coast callers should factor in the three-hour lead when placing early-morning calls to Huntington or Hamptons contacts.

Growing your Long Island reach with a 631 number

Suffolk County's economy spans industries rarely found within a single area code — world-class national laboratory science, one of the fastest-growing biotechnology corridors in the Northeast, one of the most visited luxury resort destinations in the country, and one of the largest planned industrial parks in the United States. For any business targeting these sectors, a 631 number signals authentic Long Island presence.

Reasons to choose a 631 area code number:

• Long Island Innovation Park at Hauppauge — A 1,400-acre industrial and office campus spanning Hauppauge, Ronkonkoma, and Islandia, home to approximately 1,400 companies and 55,000 jobs across advanced manufacturing, aerospace, defense technology, biotech, and information technology; as the largest industrial park of its kind in the Northeast, it represents one of the most concentrated business corridors in the entire 631 footprint
• Brookhaven National Laboratory — A U.S. Department of Energy research laboratory in Upton, Brookhaven, conducting research in physics, energy science, biology, and advanced materials; its presence anchors a research and technology ecosystem that extends through partnerships with Stony Brook University and Cold Spring Harbor Laboratory
• Biotechnology and life sciences — Stony Brook University's Center for Biotechnology, in partnership with Brookhaven National Laboratory, Cold Spring Harbor Laboratory, and the Feinstein Institutes for Medical Research, anchors the Long Island Bioscience Hub, which has attracted major state investment toward establishing the region as the Northeast's leading cell and gene therapy research corridor
• Hamptons and East End tourism — Southampton, East Hampton, Montauk, and the North Fork wine country collectively generate billions in annual economic activity through hospitality, retail, food and beverage, real estate, and seasonal events; the 631 territory's East End represents one of the highest-income seasonal markets in the country
• UCaaS virtual expansion — Businesses that serve Long Island's technology, healthcare, and professional services markets can establish immediate 631 credibility through a Unified Communications as a Service (UCaaS) platform — which bundles voice, video, messaging, and call analytics into a single cloud-hosted number — routing every inbound 631 call to any device anywhere in the world without a physical Suffolk County office; this approach is equally effective for firms building a Northeast corridor presence across multiple markets, just as a virtual 475 area code number establishes simultaneous credibility in Connecticut's Fairfield and New Haven county markets

Phone scams tied to the 631 area code

The 631 area code is actively spoofed by scammers who exploit its Long Island association to appear local to Nassau and Suffolk county residents, businesses, and seasonal visitors. Prerecorded voice calls — robocalls — account for more than half of all spam complaints associated with the 631 prefix, making Suffolk County one of the more heavily targeted territories in the New York metro area.

Common scam types tied to 631 numbers:

• Auto warranty extension calls — Automated calls claiming a vehicle warranty has expired or is about to lapse, pressing recipients for payment or personal details to extend coverage; the single most frequently reported scam type in the 631 area code, accounting for nearly 12 percent of all spam complaints, and particularly prevalent across the county's large commuter population
• Mortgage loan and real estate fraud — Callers posing as lenders, refinancing specialists, or real estate investment firms, collecting financial information under the pretext of offering below-market rates; reported at elevated rates across the 631 territory, where high home values and active real estate markets make mortgage-themed bait especially effective
• Social Security suspension fraud — Automated calls claiming a Social Security number has been compromised or suspended due to criminal activity, targeting the county's significant retired and fixed-income population across communities in Babylon, Islip, and eastern Suffolk
• Medicare and Medicaid fraud — Callers posing as Stony Brook Medicine, Northwell Health, or federal Medicare representatives, requesting insurance card numbers, Social Security digits, or co-payment details under the pretext of updating coverage or processing a benefit
• Credit card debt and bank impersonation — Callers posing as bank fraud departments or credit card issuers, claiming suspicious activity on an account and pressing for card numbers, PIN codes, or online banking credentials to fabricate a resolution process

How to protect yourself:

• Let unrecognized 631 calls go to voicemail — legitimate lenders, government agencies, and healthcare providers always leave a message and never demand immediate payment by gift card, wire transfer, or cryptocurrency
• Auto warranty extension calls are always scams — no legitimate auto manufacturer or dealer initiates unsolicited calls demanding payment to extend coverage
• Hang up and call the institution directly using the official number on your statement, insurance card, or the organization's website — never the number the caller provides
• Report suspected 631 scam calls to the FTC at reportfraud.ftc.gov and to the New York Attorney General at ag.ny.gov

631 area code fast facts

• Area code 631 covers all of Suffolk County on Long Island, including Huntington, Babylon, Islip, Smithtown, Brookhaven, Southampton, East Hampton, Riverhead, Southold, and Shelter Island
• It was created on November 1, 1999, as a geographic split from area code 516; Nassau County retained 516 and Suffolk County received 631
• Ten-digit dialing has been mandatory across the 631/934 territory since June 18, 2016, when overlay area code 934 was introduced on July 16, 2016
• The entire 631 region observes Eastern Time — the same zone as New York City, one hour ahead of Chicago and three hours ahead of the Pacific Coast
• No existing 631 numbers changed when 934 was introduced — 934 is assigned exclusively to new lines and subscriptions activated after July 16, 2016
• The economy is anchored by Long Island Innovation Park at Hauppauge, Brookhaven National Laboratory, Stony Brook University, the Long Island Bioscience Hub, and the Hamptons tourism economy
• Common scam types include auto warranty calls, mortgage loan fraud, Social Security suspension fraud, Medicare impersonation, and credit card debt scams

Frequently asked questions