Where is Middlesex County?

3 Middlesex Counties in 3 states · 2.6 million people (2025)

There are 3 counties named Middlesex County in the United States, in Massachusetts, New Jersey and Virginia. The most populous is Middlesex County, Massachusetts (county seat: Cambridge, Lowell), with 1,669,979 people in 2025. 3 of them are named after Middlesex, historic county of England.

Map of the United States showing where all 3 Middlesex Counties are, labeled by state
Every Middlesex County in the United States (red), labeled with its state. Boundaries: U.S. Census Bureau, 2025. Free to use with attribution (CC BY 4.0).

All 3 Middlesex Counties

Sorted by state. Each link opens the county's map.

StateCounty seatPopulation 2025Land area (sq mi)EstablishedNamed after
Middlesex County, MassachusettsCambridge, Lowell1,669,9798181643Middlesex
Middlesex County, New JerseyNew Brunswick883,3353091683Middlesex
Middlesex County, VirginiaSaluda10,841130–Middlesex

Questions about Middlesex Counties

How many Middlesex Counties are there?

There are 3 Middlesex Counties in the United States, in Massachusetts, New Jersey and Virginia.

Which Middlesex County is the largest?

By population, Middlesex County, Massachusetts (1,669,979 people in 2025). By land area, Middlesex County, Massachusetts (818 sq mi).

Which Middlesex County is the oldest?

Middlesex County, Massachusetts, established in 1643. The newest is Middlesex County, New Jersey (1683).

Why are there so many Middlesex Counties?

3 of the 3 are named after Middlesex, historic county of England. Many counties took their names from the same founders, presidents and generals as new states were organized.

How do I find out which Middlesex County an address is in?

Open the county map of the state: it has a search box for cities, towns and ZIP codes. On a phone, the "what county am I in" tool on our sister site uses your location.

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Other common county names