County Maps US

Middlesex County, Massachusetts

The most populous of Massachusetts's 14 counties.

CountyFIPS 25017

Within Massachusetts
Middlesex County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Cambridge, the county seat, located via the 2025 Census Gazetteer.

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Population
1,669,979
+45,518 (+2.8%) since 2020
Land area
817.9
square miles. A further 3.4% of the total area is water
Population density
2,042
people per square mile, computed rather than published
County seat
Cambridge
Middlesex County has no county government.
Established
1643
382 years ago
Largest city
Cambridge city
Population 122,588.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of Middlesex County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of Middlesex County, Massachusetts from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 800 by 725 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where Middlesex County ranks

Position among the 14 counties of Massachusetts, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn MassachusettsNationally
Population1,669,9791st of 1420th of 3,144
Land area817.9 sq mi3rd of 141,034th of 3,144
Population density2,042 per sq mi2nd of 1473rd of 3,144
Median household income$130,8472nd of 1429th of 3,143

Full data for Middlesex County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population1,669,979Vintage 2025 Population Estimates
Population in 20201,624,461Vintage 2025 Population Estimates
2020 estimates base?1,631,912Vintage 2025 Population Estimates
Land area817.9 sq mi2025 Gazetteer Files
Water area29.0 sq mi2025 Gazetteer Files
Total area847 sq mi2025 Gazetteer Files
Population density?2,042 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$130,847American Community Survey 2020-2024 5-Year Estimates
Median home value$727,800American Community Survey 2020-2024 5-Year Estimates
Median age38.9American Community Survey 2020-2024 5-Year Estimates
Households634,215American Community Survey 2020-2024 5-Year Estimates
Housing units664,267American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
+4,048
15,687 births, 11,639 deaths
Net migration
+1,924
More people moved in than moved out.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 5 areas bordering Middlesex County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Worcester CountyMassachusetts83 mi888,502
Essex CountyMassachusetts39 mi826,653
Hillsborough CountyNew Hampshire34 mi433,415
Norfolk CountyMassachusetts32 mi739,749
Suffolk CountyMassachusetts21 mi791,891

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

Side by side

All 14 counties of Massachusetts

Open the interactive Massachusetts county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.