631 Area Code – Suffolk County, New York: Location, Time Zone & History

Area code 631 traces a numbering lineage that runs through three area codes before settling into its current form. Suffolk County, along with Nassau County, was originally folded into area code 914 in 1947 under AT&T's first nationwide numbering plan, then split off into area code 516 in 1951. Growth in cellular service eventually pushed 516 toward exhaustion, and on November 1, 1999, Suffolk County was separated and assigned 631 on its own, leaving Nassau County behind in 516.

Demand kept climbing even after that split. By 2016, Suffolk County needed further relief, and area code 934 was introduced on July 16 of that year as an overlay -- the first overlay anywhere in New York State outside New York City. Mandatory ten-digit local dialing had already taken effect that June to prepare residents for the change.

Beyond its numbering history, the region blends scientific research with seasonal tourism. Brookhaven National Laboratory in Upton has been tied to multiple Nobel Prize-winning discoveries in physics, while the Hamptons on the South Fork remain known for summer visitors and celebrity homeowners. The territory also reaches Babylon, Huntington, Islip, and Riverhead, alongside industries in manufacturing, agriculture, and commercial fishing.