When was Middlesex County founded?

Middlesex County was founded in 1643, and named after Middlesex, England.

What is the county seat of Middlesex County?

The county seat of Middlesex County is Cambridge and Lowell.

Is there an online parcel map for Middlesex County?

Yes. MassGIS (Bureau of Geographic Information), Commonwealth of Massachusetts publishes a parcel map of 426,462 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 1643. Since then the Atlas of Historical County Boundaries records 31 later changes, most of them small boundary adjustments, chiefly involving Worcester County, Suffolk County and Essex 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 25017

Middlesex CountyMassachusetts

Middlesex County is one of the original four counties established in Massachusetts on May 10, 1643. The county is named after Middlesex and has Cambridge and Lowell as its county seats.

Founded1643
County seatCambridge and Lowell
Named forMiddlesex, England
Land area818 sq mi + 29 sq mi water
Population1,632,002 2020 Census
Parcels mapped426,462 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 Massachusetts

Massachusetts has 14 counties and county equivalents, each with its own records office. Shapes with a page are links.

Counties of Massachusetts · Middlesex highlighted

History

Founded in 1643

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

Middlesex County was created as one of four original counties in Massachusetts in 1643. Over its early history, the county exchanged and lost land to the creation of Worcester County in 1731 and subsequent boundary adjustments with Worcester and Norfolk counties.

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

1643
Middlesex County created Middlesex created as one of four original counties in Massachusetts. 10 May 1643 · Mass. Recs., 2:38
1731
Lost territory Middlesex lost to creation of Worcester.
to Worcester
10 July 1731 · Mass. Col. Acts, vol. 2, ch. 8 [1730-1731], sec. 1/p. 584
1732
Exchanged territory Middlesex exchanged with Worcester when town of Harvard was created from towns of Groton, Lancaster, and Stow.
with Worcester
29 June 1732 · Mass. Col. Acts, vol. 2, ch. 4 [1732-1733], sec. 1/p. 644
1783
Gained territory Middlesex gained from Worcester when town of Boxborough gained from town of Harvard.
from Worcester
25 February 1783 · Mass. Acts 1783, ch. 8, sec. 1/p. 214
1792
Gained territory Middlesex gained from Worcester when town of Ashby gained from town of Ashburnham.
from Worcester
16 November 1792 · Mass. Acts 1792, ch. 2, sec. 1/p. 224

Show all 45 changes (40 more, mostly small adjustments)

1643
Middlesex County created Middlesex created as one of four original counties in Massachusetts. 10 May 1643 · Mass. Recs., 2:38
1658
Lost territory Middlesex lost small area (15 acres) to Essex when town of Andover gained from town of Billerica.
to Essex
26 May 1658 · Mass. Recs., vol. 4, pt. 1:333
1691
Changed Middlesex continued under the new Massachusetts Bay provincial charter issued by King William Iii and Queen Mary Ii (no change).
IiiIi
7 October 1691 · Mass. Col. Acts, vol. 1, ch. 27 [1692-1693], sec. 1/p. 63; Swindler, 5:80
1731
Lost territory Middlesex lost to creation of Worcester.
to Worcester
10 July 1731 · Mass. Col. Acts, vol. 2, ch. 8 [1730-1731], sec. 1/p. 584
1732
Exchanged territory Middlesex exchanged with Worcester when town of Harvard was created from towns of Groton, Lancaster, and Stow.
with Worcester
29 June 1732 · Mass. Col. Acts, vol. 2, ch. 4 [1732-1733], sec. 1/p. 644
1735
Lost territory Middlesex lost small area to Worcester when town of Upton was created from town of Hopkinton.
to Worcester
14 June 1735 · Mass. Col. Acts, vol. 2, ch. 11 [1735-1736], sec. 1/p. 764
1767
Gained territory Middlesex gained small area from Worcester when town of Ashby was created from towns of Fitchburg and Ashburnham.
from Worcester
6 March 1767 · Mass. Col. Acts, vol. 4, ch. 15 [1766-1767]/p. 908
1783
Gained territory Middlesex gained from Worcester when town of Boxborough gained from town of Harvard.
from Worcester
25 February 1783 · Mass. Acts 1783, ch. 8, sec. 1/p. 214
1784
Lost territory Middlesex lost small area to Worcester when town of Berlin was created from towns of Marlborough, Northborough, and Bolton.
to Worcester
16 March 1784 · Mass. Acts 1784, ch. 23, sec. 1/p. 98
1786
Lost territory Middlesex lost small area to Worcester when town of Southborough gained from town of Framingham.
to Worcester
7 March 1786 · Mass. Acts 1786, ch. 21, sec. 1/p. 410
1792
Boundary clarified Boundary between Middlesex and Suffolk was redefined in part when the boundary between towns of Medway and Sherburne was redefined (no change).
with Suffolkno change
3 March 1792 · Mass. Acts 1792, ch. 23, sec. 1/p. 155
1792
Gained territory Middlesex gained from Worcester when town of Ashby gained from town of Ashburnham.
from Worcester
16 November 1792 · Mass. Acts 1792, ch. 2, sec. 1/p. 224
1797
Exchanged territory Middlesex exchanged with Norfolk when town of Natick exchanged with town of Needham.
with Norfolk
22 June 1797 · Mass. Acts 1797, ch. 22, sec. 1/p. 142
1807
Lost territory Middlesex lost small area to Worcester when town of Northborough gained from town of Marlborough.
to Worcester
20 June 1807 · Mass. Acts 1807, p. 52
1808
Lost territory Middlesex lost small area to Worcester when town of Upton gained from town of Hopkinton to accommodate local property owner.
to Worcester
8 March 1808 · Mass. Acts 1808, ch. 106, sec. 1/p. 336
1829
Lost territory Middlesex lost small area (one acre) to Worcester when town of Bolton gained from town of Marlborough to accommodate local property owner.
to Worcester
11 February 1829 · Mass. Acts 1829, ch. 47/p. 72
1829
Gained territory Middlesex gained small area from Worcester when town of Ashby gained from town of Fitchburg to accommodate local property owner; Middlesex exchanged with Norfolk when town of Holliston gained from town of Medway.
from Worcester from Norfolk
3 March 1829 · Mass. Acts 1829, ch. 125/p. 200 and ch. 133/p. 209
1835
Exchanged territory Middlesex exchanged with Worcester when towns of Holliston, Hopkinton, and Milford exchanged territory.
with Worcester
27 March 1835 · Mass. Acts 1835, ch. 72/p. 382
1838
Boundary clarified Boundary between Middlesex and Worcester was redefined in part when line between towns of Marlborough and Bolton was redefined (no change).
with Worcesterno change
16 March 1838 · Mass. Acts 1838, ch. 36/p. 330
1838
Lost territory Middlesex lost to Norfolk when town of Roxbury gained from town of Newton.
to Norfolk
23 April 1838 · Mass. Acts 1838, ch. 167, sec. 1/p. 481
1843
Gained territory Middlesex gained small area from Worcester when town of Marlborough gained from town of Southborough to accommodate local property owners.
from Worcester
24 March 1843 · Mass. Acts 1843, ch. 89, sec. 1/p. 53
1846
Boundary clarified Boundary between Middlesex and Worcester was redefined in part when line between towns of Shirley and Lunenburg was redefined (no change).
with Worcesterno change
3 March 1846 · Mass. Acts 1846, ch. 74/p. 35
1848
Boundary clarified Boundary between Middlesex and Worcester was redefined in part when line between towns of Shirley and Lunenburg was redefined (no change).
with Worcesterno change
25 April 1848 · Mass. Acts 1848, ch. 194, sec. 1/p. 708
1854
Gained territory Middlesex gained small area from Essex when town of Reading gained from town of Lynnfield.
from Essex
10 April 1854 · Mass. Acts 1854, ch. 246, sec. 1/p. 163
1858
Gained territory Middlesex gained from Essex when town of North Reading gained from town of Lynnfield.
from Essex
7 January 1858 · Mass. Acts 1857, ch. 238, sec. 1/p. 572; Mass. Sec. Comm., 41
1859
Lost territory Middlesex lost small area to Worcester when town of Milford gained from town of Holliston.
to Worcester
1 April 1859 · Mass. Acts 1859, ch. 149/p. 312
1868
Gained territory Middlesex gained from Worcester when town of Hudson gained from town of Bolton.
from Worcester
20 March 1868 · Mass. Acts 1868, ch. 79, sec. 1/p. 62
1874
Lost territory Middlesex lost to Suffolk when Boston gained all of Brighton and Charlestown.
to Suffolk
5 January 1874 · Mass. Acts 1873, ch. 286, sec. 1/p. 716, ch. 303, sec. 1/p. 747, and ch. 314, sec. 1/p. 810
1874
Changed Boundary between Middlesex and Suffolk was adjusted when line between Boston and Newton was adjusted.
Suffolk
29 May 1874 · Mass. Acts 1874, ch. 277, sec. 1/p. 189
1875
Gained territory Middlesex gained small area from Suffolk when Newton gained from Boston.
from Suffolk
1 July 1875 · Mass. Acts 1875, ch. 184, sec. 1/p. 773
1891
Changed Boundary between Middlesex and Suffolk was adjusted when line between Boston and Somerville was adjusted.
Suffolk
4 May 1891 · Mass. Acts 1891, ch. 294, sec. 1/p. 856
1898
Changed Boundary between Middlesex and Suffolk was adjusted when line through the Charles River between Boston and Cambridge was adjusted, and line between Boston and Newton was adjusted.
Suffolk
29 March 1898 · Mass. Acts 1898, ch. 242, sec. 1/p. 178 and ch. 243/p. 179
1898
Changed Boundary between Middlesex and Suffolk was adjusted when line between Boston and Newton was adjusted.
Suffolk
13 May 1898 · Mass. Acts 1898, ch. 431, sec. 1/p. 376
1901
Boundary clarified Boundary between Middlesex and Worcester was redefined when line between towns of Marlborough and Southborough was redefined (no change).
with Worcesterno change
16 May 1901 · Mass. Acts 1901, ch. 393, sec. 1/p. 306
1903
Boundary clarified Boundary between Middlesex and Essex was redefined in part when line between towns of Tewkesbury and Andover was redefined (no change).
with Essexno change
21 May 1903 · Mass. Acts 1903, ch. 373, sec. 1/p. 343
1904
Boundary clarified Boundary between Middlesex and Essex was redefined in part when line between towns of North Andover and North Reading was redefined (no change).
with Essexno change
12 March 1904 · Mass. Acts 1904, ch. 149, sec. 1/p. 98
1904
Boundary clarified Boundary between Middlesex and Essex was redefined in part when line between towns of North Reading and Andover was redefined (no change).
with Essexno change
22 April 1904 · Mass. Acts 1904, ch. 250, sec. 1/p. 213
1905
Boundary clarified Boundary between Middlesex and Worcester was redefined in part when line between towns of Berlin and Hudson was redefined (no change), and when line between towns of Marlborough and Berlin was adjusted.
with Worcesterno change
1 May 1905 · Mass. Acts 1905, ch. 357, sec. 1/p. 283 and ch. 358, sec. 1/p. 284
1905
Boundary clarified Boundary between Middlesex and Essex was redefined in part when line between towns of Lynnfield and Reading was redefined (no change).
with Essexno change
2 May 1905 · Mass. Acts 1905, ch. 361, sec. 1/p. 286
1906
Gained territory Middlesex gained small area from Worcester when towns of Boxborough and Littleton gained from town of Harvard.
from Worcester
14 June 1906 · Mass. Acts 1906, ch. 483, sec. 1/p. 654 and ch. 484, sec. 1/p. 655
1907
Boundary clarified Boundary between Middlesex and Norfolk was redefined in part when line between towns of Newton and Brookline was redefined (no change).
with Norfolkno change
28 March 1907 · Mass. Acts 1907, ch. 249, sec. 1/p. 194
1907
Boundary clarified Boundary between Middlesex and Worcester was redefined in part when town of Hopkinton's boundary with towns of Milford and Upton was redefined (no change).
with Worcesterno change
16 May 1907 · Mass. Acts 1907, ch. 423, sec. 1 and ch. 424, sec. 1/pp. 362-363
1910
Changed Boundary between Middlesex and Suffolk was adjusted when line in the Charles River between Boston and Cambridge was adjusted.
Suffolk
29 March 1910 · Mass. Acts 1910, ch. 312, sec. 1/p. 239
1933
Gained territory Middlesex gained small area from Essex when town of Wakefield gained from town of Saugus.
from Essex
18 September 1933 · Mass. Acts 1933, ch. 298, sec. 1/p. 453; Mass. Sec. Comm., 59
1947
Exchanged territory Middlesex exchanged small areas with Essex when town of Lynnfield exchanged with town of Reading.
with Essex
10 April 1947 · Mass. Acts 1947, ch. 243, sec. 1/p. 222

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 426,462 parcels from MassGIS (Bureau of Geographic Information), Commonwealth of Massachusetts. 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, 817,486 in all from MassGIS.
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

1,632,002 2020 Census count

Housing units

658,283 2020 Census count

Land area

818 square miles

Water area

29 square miles

People per sq mi

1,995 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.

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Questions

Common questions about Middlesex County

When was Middlesex County founded?: Middlesex County was founded in 1643, and named after Middlesex, England.
What is the county seat of Middlesex County?: The county seat of Middlesex County is Cambridge and Lowell.
Is there an online parcel map for Middlesex County?: Yes. MassGIS (Bureau of Geographic Information), Commonwealth of Massachusetts publishes a parcel map of 426,462 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 1643. Since then the Atlas of Historical County Boundaries records 31 later changes, most of them small boundary adjustments, chiefly involving Worcester County, Suffolk County and Essex 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