Middlesex County, New Jersey

County seat: New Brunswick · Population 883,335 (2025) · 309 sq mi

Middlesex County is the 3rd most populous of New Jersey's 21 counties, with 883,335 people (2025 estimate). Its county seat is New Brunswick. The map shows its 15 cities and towns and the 5 neighboring counties.

Map of Middlesex County, New Jersey with cities, towns and the county boundary
Middlesex County, New Jersey with its cities and towns, unincorporated communities (CDPs) and neighboring counties. Boundaries: U.S. Census Bureau, 2025. Free to use with attribution (CC BY 4.0).
Download PDF (Letter) 212 KBPNG image 155 KBNew Jersey county map

Middlesex County facts

County seat
New Brunswick
Population (2025 estimate)
883,335 +2.3% since 2020
Land area
309 sq mi 12th largest of 21
Water area
14 sq mi
Population density
2,856 per sq mi
Established
1683
Same name
One of 3 Middlesex Counties in the US
Named after
Middlesex historic county of England
Largest city
Edison 109,077
Median household income
$111,549
Cities and towns
15 plus 36 CDPs
ZIP codes
44
Time zone
Eastern
FIPS code
34023

Cities and towns in Middlesex County

Middlesex County has 15 incorporated cities, towns and villages. Populations count the people living inside Middlesex County; cities that cross a county line also list the other counties.

NameTypePopulation 2025Also in
New Brunswick (county seat)City57,133
Perth AmboyCity56,739
SayrevilleBorough46,787
CarteretBorough25,781
South PlainfieldBorough24,891
South RiverBorough16,262
MetuchenBorough15,363
Highland ParkBorough15,259
MiddlesexBorough14,740
South AmboyCity10,403
DunellenBorough8,337
SpotswoodBorough8,236
MilltownBorough7,103
JamesburgBorough5,819
HelmettaBorough2,474

Unincorporated communities (CDPs)

Census-designated places are communities without their own city government; the county provides their services.

CommunityPopulationAlso in
Old Bridge28,236
Woodbridge20,756
Iselin19,551
Colonia18,587
Avenel17,121
Princeton Meadows15,561
Fords12,771
Kendall Park10,011
Monmouth Junction9,141
Madison Park9,124
Dayton7,952
Heathcote7,717
Laurence Harbor6,191
Rutgers University-Busch Campus5,920
Port Reading3,511
Hopelawn3,496
Rossmoor3,350
Rutgers University-Livingston Campus3,258
Sewaren3,248
Menlo Park Terrace3,062
Plainsboro Center2,773
Concordia2,611
Whittingham2,480
Brownville2,377
Clearbrook2,375
Monroe Manor2,286
Keasbey2,252
Cranbury2,185
Forsgate2,102
Regency at Monroe1,991
Stonebridge1,966
Kingston1,510Somerset County
Deans1,154
The Ponds1,097
Encore at Monroe872
Renaissance at Monroe581

ZIP codes in Middlesex County

44 ZIP codes reach into Middlesex County. ZIP codes ignore county lines, so some also cover a neighboring county.

Population of Middlesex County, 2020–2025

Middlesex County grew by 20,110 people (+2.3%) between April 2020 and July 2025: 9,978 more births than deaths and a net gain of 9,370 people from migration.

Year (July 1)Population
2020861,248
2021861,965
2022864,552
2023873,281
2024881,620
2025883,335

Neighboring counties

Printable Middlesex County map

The PDF is a vector file with real text: it prints sharp on Letter paper and you can search it for a town. The PNG is 2400 pixels wide for slides and documents. Both are free to use with a credit to WhichCounty.

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Sources

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