When was Middlesex County founded?

Middlesex County was founded in 1683, and named after Middlesex, England.

What is the county seat of Middlesex County?

The county seat of Middlesex County is New Brunswick.

Is there an online parcel map for Middlesex County?

Yes. A public source publishes a parcel map of 275,925 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has Middlesex County's boundary or name changed?

Middlesex County was created in 1683. Since then the Atlas of Historical County Boundaries records 16 later changes, chiefly involving Somerset County, Monmouth County and Union County.

Is my lot in a flood zone?

We do not have flood maps for Middlesex County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

County · code 34023

Middlesex CountyNew Jersey

Middlesex County is a county in New Jersey with its seat in New Brunswick. It was created on March 7, 1683, as one of four original counties in East New Jersey.

Founded1683
County seatNew Brunswick
Named forMiddlesex, England
Land area309 sq mi + 14 sq mi water
Population863,162 2020 Census
Parcels mapped275,925 checked 15 October 2026

Open the free map Click any parcel in Middlesex County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated 20 October 2026

Census outline · seat marked

History

Founded in 1683

An old deed may name a county that no longer exists, or a boundary that has since moved.

Middlesex County was created on March 7, 1683, as one of four original counties in East New Jersey. On January 8, 1686/1687, Middlesex gained land from Non-County Area (West) and from Burlington Court in the Indefinite Counties Area when commissioners from East and West New Jersey agreed on a new division, with the southern part of this line becoming known as the Keith Line. Middlesex lost territory to the creation of Somerset County in 1688, to the creation of Mercer County in 1838, and exchanged boundaries multiple times with Monmouth County between 1710 and 1847. When the proprietors of East and West New Jersey surrendered their rights to Queen Anne in 1702, the two colonies were united into the single royal province of New Jersey, and Middlesex became a county in that province.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries; the 5 that matter most are shown first.

1683
Middlesex County created 7 March 1682/1683. Middlesex was created as one of four original counties in East New Jersey; Non-County Area (East) eliminated. 7 March 1683 · Shaw, 1:212, 231; Snyder, 10-11, 29-31; Wall and Pickersgill, 1:63
1687
Gained territory 8 January 1686/1687. Middlesex gained from Non-County Area (West) and from Burlington Court in the Indefinite Counties Area in the southern part of West New Jersey when commissioners from East and West New Jersey agreed on a new division between their colonies. The line ran west of the boundary specified in the Quintipartite Deed of 1676. The southern part of this line was demarcated in the spring of 1687 and became known as the Keith Line, named for the surveyor. 8 January 1687 · Snyder, 9, 31
1688
Lost territory Middlesex lost to the creation of Somerset. Somerset was not fully organized, attached to Middlesex.
to Somerset
14 May 1688 · Leaming and Spicer, 305; Snyder, 12, 29
1702
Became part of New Jersey Proprietors of East and West New Jersey surrendered to Queen Anne their rights to govern their colonies, and the two colonies were united into the single royal province of New Jersey. Middlesex became a county in the royal province of New Jersey; boundaries were unchanged. 17 April 1702 · Pomfret, Colonial New Jersey, 87; Snyder, 13; Swindler, 6:439-445, Van Zandt, 79
1710
Lost territory 21 January 1709/1710. Middlesex lost to Somerset and exchanged with Monmouth.
to Somerset to Monmouth
21 January 1710 · Paterson, 2-4; Snyder, 30-32

Show all 22 changes (17 more, mostly small adjustments)

1683
Middlesex County created 7 March 1682/1683. Middlesex was created as one of four original counties in East New Jersey; Non-County Area (East) eliminated. 7 March 1683 · Shaw, 1:212, 231; Snyder, 10-11, 29-31; Wall and Pickersgill, 1:63
1687
Gained territory 8 January 1686/1687. Middlesex gained from Non-County Area (West) and from Burlington Court in the Indefinite Counties Area in the southern part of West New Jersey when commissioners from East and West New Jersey agreed on a new division between their colonies. The line ran west of the boundary specified in the Quintipartite Deed of 1676. The southern part of this line was demarcated in the spring of 1687 and became known as the Keith Line, named for the surveyor. 8 January 1687 · Snyder, 9, 31
1688
Lost territory Middlesex lost to the creation of Somerset. Somerset was not fully organized, attached to Middlesex.
to Somerset
14 May 1688 · Leaming and Spicer, 305; Snyder, 12, 29
1702
Became part of New Jersey Proprietors of East and West New Jersey surrendered to Queen Anne their rights to govern their colonies, and the two colonies were united into the single royal province of New Jersey. Middlesex became a county in the royal province of New Jersey; boundaries were unchanged. 17 April 1702 · Pomfret, Colonial New Jersey, 87; Snyder, 13; Swindler, 6:439-445, Van Zandt, 79
1710
Lost territory 21 January 1709/1710. Middlesex lost to Somerset and exchanged with Monmouth.
to Somerset to Monmouth
21 January 1710 · Paterson, 2-4; Snyder, 30-32
1714
Gained territory 15 March 1713/1714. Middlesex gained from Somerset.
from Somerset
15 March 1714 · Paterson, 4-5; Snyder, 32
1714
Changed In 1714, Somerset was fully organized, detached from Middlesex.
Somerset
31 December 1714 · Snell, 568
1790
Boundary clarified Boundary between Middlesex and Somerset clarified (no change).
with Somersetno change
24 November 1790 · Paterson, 103; Snyder, 34
1822
Boundary clarified Water boundaries of Middlesex, Essex, and Monmouth were redefined to assert New Jersey's claim to the western half of Arthur Kill, the water separating Staten Island, N.Y., from the New Jersey mainland.
with Essex with Monmouthwith N.y.no change
28 November 1822 · N.J. Acts 1822, p. 35; Snyder, 34-36
1838
Lost territory Middlesex lost to the creation of Mercer.
to Mercer
22 February 1838 · N.J. Acts 1838, p. 99; Snyder, 37
1844
Lost territory Middlesex lost to Monmouth.
to Monmouth
28 February 1844 · N.J. Acts 1844, p. 141; Snyder, 38
1845
Gained territory Middlesex gained from Monmouth.
from Monmouth
21 March 1845 · N.J. Acts 1845, p. 148; Snyder, 38
1847
Lost territory Middlesex lost to Monmouth.
to Monmouth
24 February 1847 · N.J. Acts 1847, p. 86; Snyder, 40
1850
Gained territory Middlesex gained from Somerset.
from Somerset
1 February 1850 · N.J. Acts 1858, pp. 5-6; Snyder, 40
1851
Boundary clarified Middlesex water boundary redefined.
no change
18 March 1851 · N.J. Acts 1851, p. 369
1855
Lost territory Middlesex lost small areas to Somerset along road between Kingston and New Brunswick.
to Somerset
29 March 1855 · N.J. Acts 1855, pp. 490-491; Snyder, 40-41, 169, 175
1858
Exchanged territory Middlesex exchanged small areas with Somerset along road between Kingston and New Brunswick.
with Somerset
6 February 1858 · N.J. Acts 1858, p. 29; Snyder, 42, 169, 175, 221, 227
1860
Lost territory Middlesex lost to Union.
to Union
16 February 1860 · N.J. Acts 1860, p. 97; Snyder, 42
1871
Gained territory Middlesex gained small area from Union.
from Union
5 April 1871 · N.J. Acts 1871, pp. 1255-1256; Snyder, 42
1878
Boundary clarified Boundary between Middlesex and Somerset redefined (no change).
with Somersetno change
29 March 1878 · N.J. Acts 1878, pp. 568-569; Snyder, 43
1892
Boundary clarified Water boundaries of Middlesex, Bergen, Hudson, Monmouth, and Union redefined to match the New Jersey-New York interstate boundary agreement of 1834, as detailed by joint commissions in 1887 and 1899.
with Bergen with Hudson with Monmouth with Unionno change
9 April 1892 · N.J. Acts 1892, p. 441; Snyder, 44-45
1939
Lost territory Middlesex lost small area in Madison township to Monmouth.
to Monmouth
18 July 1939 · N.J. Acts 1939, p. 657; Snyder, 47

Land and parcels

What the maps cover in Middlesex

Who publishes each layer, how good it is, and when we last checked.

Parcels Good enough

Lot lines and tax-map numbers for 275,925 parcels. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
checked 15 October 2026
Address points Official

One point per address, 326,993 in all from NJOGIS.
edited 23 September 2026 · checked 14 October 2026
Buildings Reference

Roof outlines traced from aerial imagery from FEMA Response Geospatial Office with Oak Ridge National Laboratory (ORNL). Good for seeing what is on a lot; not accurate enough to set a fence from.
checked 18 October 2026

Official: from the office that keeps the record
Good enough: a reliable statewide or national copy
Fallback: a guide only; check the official record
Missing: nothing public found yet

People and land

Middlesex by the Census

Population

863,162 2020 Census count

Housing units

315,521 2020 Census count

Land area

309 square miles

Water area

14 square miles

People per sq mi

2,791 population ÷ land area

Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.

Rules and offices

Middlesex County's official site

We have found the county's site but not its offices yet; start there.

County government

County government
The official website of Middlesex County.
co.middlesex.nj.us

See your own lot on these maps

Open Middlesex County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.

Open the free map no sign-in Pro early access

Questions

Common questions about Middlesex County

When was Middlesex County founded?: Middlesex County was founded in 1683, and named after Middlesex, England.
What is the county seat of Middlesex County?: The county seat of Middlesex County is New Brunswick.
Is there an online parcel map for Middlesex County?: Yes. A public source publishes a parcel map of 275,925 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Middlesex County's boundary or name changed?: Middlesex County was created in 1683. Since then the Atlas of Historical County Boundaries records 16 later changes, chiefly involving Somerset County, Monmouth County and Union County.
Is my lot in a flood zone?: We do not have flood maps for Middlesex County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby