When was Middlesex County founded?

Middlesex County was founded in 1785, formed from Hartford County and New London County, and named after Middlesex, England.

What is the county seat of Middlesex County?

The county seat of Middlesex County is Middletown.

Is there an online parcel map for Middlesex County?

Yes. A public source publishes a parcel map of 77,965 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 1785 from Hartford County and New London County. Since then the Atlas of Historical County Boundaries records 1 later change, chiefly involving New Haven 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 09007

Middlesex CountyConnecticut

Middlesex County is located in Connecticut with its county seat in Middletown. It was created on May 12, 1785, from parts of Hartford and New London counties.

Founded1785
County seatMiddletown
Named forMiddlesex, England
Land area369 sq mi + 70 sq mi water
Population164,245 2020 Census
Parcels mapped77,965 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 19 October 2026

Census outline · seat marked

Where it is

Middlesex on the map of Connecticut

Connecticut has 8 counties and county equivalents, each with its own records office. Shapes with a page are links.

Counties of Connecticut · Middlesex highlighted

History

Formed in 1785 from Hartford County and New London County

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

Middlesex County was created in 1785 from Hartford and New London counties. In 1799, the county gained the town of Durham from New Haven County.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries.

1785
Middlesex County created Middlesex created from Hartford and New London.
from Hartford from New London
12 May 1785 · Conn. St. Recs., 6:10-11
1796
Boundary clarified Middlesex boundaries were redefined (no change).
no change
31 October 1796 · Conn. Pub. Acts 1796, pp. 123-124
1799
Gained territory Middlesex gained town of Durham from New Haven.
from New Haven
9 May 1799 · Conn. St. Recs., 9:351
1881
Boundary clarified Middlesex jurisdiction over the waters of Long Island Sound was redefined, in accordance with the redefinition of the state line that took effect 26 February 1881 (no change).
no change
22 March 1881 · Conn. Pub. Acts 1881, ch. 37, sec. 1/p. 19

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 77,965 parcels. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
edited 6 October 2026 · checked 15 October 2026
Address points Missing

No public address points layer found for Middlesex County yet.
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

164,245 2020 Census count

Housing units

76,289 2020 Census count

Land area

369 square miles

Water area

70 square miles

People per sq mi

445 population ÷ land area

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

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 1785, formed from Hartford County and New London County, and named after Middlesex, England.
What is the county seat of Middlesex County?: The county seat of Middlesex County is Middletown.
Is there an online parcel map for Middlesex County?: Yes. A public source publishes a parcel map of 77,965 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 1785 from Hartford County and New London County. Since then the Atlas of Historical County Boundaries records 1 later change, chiefly involving New Haven 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