857 Area Code: Boston, Massachusetts

Massachusetts's 857 area code is an overlay sharing geography with the long-running 617 across Boston and the immediately adjacent cities. Boston anchors the directory's records here, set at the bottom of Boston Harbor on a peninsula expanded by centuries of landfill. The 857 designation, part of the North American Numbering Plan, has been filling with allocations as the city's number demand has continued to grow past what 617 alone could carry, and the footprint covers the same broad inner-Boston geography that includes Cambridge, Brookline, and the immediate surrounding cities.

In records the directory has compiled for 857 numbers, other Massachusetts cities — Lowell, Quincy, Springfield, and Worcester — recur frequently. None of those are inside the 857 footprint. The pattern reflects standard public-record dynamics, with phone numbers porting across Massachusetts and addresses linked across multiple cities. The directory currently documents 172 distinct prefixes within 857 in detail, a working subset of the prefix population the code carries.

Boston's median age sits well under the US figure, at roughly the low thirties, a pattern shaped by the substantial student population at the surrounding universities. Home values run roughly twice the US median, household income comes in well above the national reading, and population places Boston among the larger New England cities. The 857 footprint shares those demographics with 617 because both codes serve the same Boston-and-inner-suburb geography in overlapping form.