Middlesex County, Massachusetts

Middlesex County is a county in Massachusetts, United States, bordering Boston on the northwest and reaching from the New Hampshire line south to the Charles River valley. It had a population of 1,632,002 at the 2020 census, an estimated 1,669,979 by 2025, and covers 818 square miles (2,120 km2) of land centred near 42°29′N 71°23′W.

Cambridge is the county seat, and Lowell serves as its second seat; together they still host the county’s trial courts and registries of deeds even though Massachusetts abolished county government here in 1997. Cambridge’s postal code is 02139. The county holds 13 cities and 41 towns, no unincorporated territory at all, and it runs on Eastern Time. Its FIPS code is 25017.

Towns & Villages in Middlesex County

Middlesex County has 54 incorporated municipalities on record: 13 cities and 41 towns. Massachusetts has no unincorporated land, so every acre of the county sits inside one of these 54 governments; villages and census-designated places (CDPs) noted afterward are subdivisions of a city or town, not separate governments.

Several of the county’s larger towns and cities contain their own named villages, which are not separate governments but are large enough to carry their own ZIP code and identity. Cambridge’s East Cambridge and Cambridgeport, Newton’s thirteen villages (Newton Centre, Auburndale, Waban and others), Wayland’s Cochituate (population 6,927 at the 2020 census, more than half of Wayland’s total), Concord’s West Concord (6,320) and Hudson’s Hudson (CDP) center (15,749) are the largest of these. Devens, a former Army post now redeveloped for housing and business, straddles Ayer and Shirley in this county along with Harvard in neighboring Worcester County; its 2020 census population was 1,697. Hanscom Air Force Base, an active-duty installation, likewise spans four Middlesex towns — Bedford, Concord, Lexington and Lincoln.

ZIP Codes

Middlesex County’s 54 cities and towns use roughly 90 ZIP codes in total, most tied one-to-one to a town name. The larger cities carry several each: Cambridge runs 02138–02142, Somerville 02143–02145, Newton 02458–02468, Waltham 02451–02454, Framingham 01701–01705 and Lowell 01850–01854. Every other town in the table above uses the single ZIP listed for its post office.

Villages inside larger towns share their parent’s code rather than issuing their own — East Cambridge mail runs through 02141, and Cochituate through Wayland’s 01778 — except where a village grew large enough to be assigned its own code, as Hudson’s town center (01749) and West Concord (01742, shared with Concord) illustrate.

Geography

Middlesex County sits in eastern Massachusetts, running from the rolling farmland and forest of its northwest corner near the New Hampshire line down through dense inner suburbs abutting Boston. Of its 847 square miles, 818 are land and 29 are water, about 3.5 percent. The Charles River forms much of the county’s southern edge and cuts through Newton and Waltham; the Concord River, formed by the meeting of the Sudbury and Assabet rivers, runs north through Concord and Billerica to join the Merrimack at Lowell. The Merrimack River itself defines Lowell’s northern waterfront. Walden Pond, in Concord, and Spot Pond, in the Middlesex Fells Reservation spanning Stoneham, Medford, Malden and Winchester, are the county’s best-known bodies of water.

Hillsborough County, New Hampshire, lies to the north. Within Massachusetts, Essex County lies to the northeast and Suffolk County, home to Boston, to the southeast; Middlesex has no live directory page for either of those two counties yet. Norfolk County lies to the south, and Worcester County to the west. Hillsborough County borders the county’s northern towns directly.

Demographics

Middlesex County had a population of 1,632,002 at the 2020 census, the highest of any county in Massachusetts or New England, and the latest county estimate puts it near 1,669,979 residents. Cambridge and Lowell are its two largest cities, each over 100,000 people, followed by Newton at 88,923 and Somerville at 81,045. Median household income for the county runs about $130,847, well above the Massachusetts statewide figure. Population density works out to roughly 1,990 people per square mile of land, among the highest of any county in New England, reflecting the county’s position inside the Boston–Cambridge–Newton metropolitan area.

Economy & Local Life

Professional, scientific and technical services employ the most workers in the county, about 159,296 people, followed by health care and social assistance at 127,654 and educational services at 121,624. Cambridge’s Kendall Square is one of the world’s densest biotechnology clusters, anchored by Moderna and Biogen, both headquartered there, alongside Harvard University and the Massachusetts Institute of Technology. Framingham is home to two Fortune 500 headquarters, TJX Companies and, for decades, Staples. MITRE Corporation, a federally funded research center, is headquartered in Bedford. Tufts University sits across Medford and Somerville, and the University of Massachusetts Lowell anchors that city’s downtown. The county’s biggest annual event is the Boston Marathon, which starts in Hopkinton each Patriots’ Day, the third Monday in April, and passes through Ashland, Framingham and Natick before leaving the county.

History

The Massachusetts General Court created Middlesex County on May 10, 1643, one of the colony’s original four shires, named for Middlesex, England, the home county of many early settlers. Cambridge and Lowell later split its courts and deed registries into Southern and Northern districts. On July 11, 1997, Massachusetts abolished the county’s executive government outright, citing its insolvency; Middlesex survives only as a geographic and judicial boundary, with an elected sheriff’s office still operating countywide.

The county’s defining historical event predates that by more than three centuries: on April 19, 1775, British regulars marching from Boston to seize colonial munitions clashed with local militia at Lexington and then at Concord’s North Bridge, opening the American Revolutionary War. Both battle sites are preserved within Minute Man National Historical Park, which spans Lexington, Concord and Lincoln.

Getting There

Interstate 95 (the Route 128 beltway) arcs through the county’s inner suburbs from Woburn to Newton. Interstate 93 crosses north–south through Medford and Woburn, Interstate 90 (the Massachusetts Turnpike) runs east–west through Newton, Weston and Framingham, and Interstate 495 forms an outer loop through Westford, Littleton and Marlborough. Route 2 crosses Cambridge, Concord and Acton, and Route 3 runs through Burlington, Billerica and Chelmsford toward New Hampshire.

• Boston — on the county’s southeastern border, reached directly from Cambridge and Somerville
• Worcester — about 35 miles southwest of Cambridge
• Nashua, New Hampshire — about 15 miles north of Lowell
• Providence, Rhode Island — about 55 miles south of Cambridge

Boston Logan International Airport, roughly six miles from Cambridge, is the region’s major commercial airport. Hanscom Field, a general-aviation airport in Bedford, sits inside the county itself. Amtrak’s Downeaster stops at the Anderson Regional Transportation Center in Woburn, and its Lake Shore Limited and other services call at Framingham station.

Frequently Asked Questions

Where is Middlesex County located?
It sits in eastern Massachusetts, bordering Boston, running north to the New Hampshire line and bordered by Essex, Suffolk, Norfolk, Worcester and Hillsborough (NH) counties.

What is the population of Middlesex County?
1,632,002 at the 2020 census, with a 2025 estimate near 1,669,979 — the most populous county in Massachusetts and New England.

How big is Middlesex County?
847 square miles (2,190 km2) in total, of which 818 square miles (2,120 km2) are land.

What is the county seat of Middlesex County?
Cambridge is the traditional county seat, and Lowell is the second seat; Massachusetts abolished county government here in 1997, so neither functions as a governing seat today.

How many towns and cities are in Middlesex County?
54 incorporated municipalities — 13 cities and 41 towns — and no unincorporated territory, since Massachusetts has none.

What ZIP codes does Middlesex County use?
About 90 codes in total; most towns use a single ZIP matching the town name, while Cambridge, Somerville, Newton, Waltham, Framingham and Lowell each use several.

What is Middlesex County known for?
The opening battles of the American Revolution at Lexington and Concord in 1775, Harvard and MIT in Cambridge, and the start of the Boston Marathon each April in Hopkinton.

More counties in this state: Towns and villages in Massachusetts.