County Maps US

Marin County, California

A county in California, ranked 26 of 58 by population.

CountyFIPS 06041

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

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Population
253,694
-7,643 (-2.9%) since 2020
Land area
520.1
square miles. A further 37.2% of the total area is water
Population density
488
people per square mile, computed rather than published
County seat
San Rafael
Seat of county government.
Established
1850
175 years ago
Largest city
San Rafael city
Population 59,410.

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 Marin 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 Marin County, California 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 762 by 800 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 Marin County ranks

Position among the 58 counties of California, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn CaliforniaNationally
Population253,69426th of 58291st of 3,144
Land area520.1 sq mi55th of 582,004th of 3,144
Population density488 per sq mi13th of 58285th of 3,144
Median household income$149,0913rd of 587th of 3,143

Full data for Marin County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population253,694Vintage 2025 Population Estimates
Population in 2020261,337Vintage 2025 Population Estimates
2020 estimates base?262,312Vintage 2025 Population Estimates
Land area520.1 sq mi2025 Gazetteer Files
Water area308 sq mi2025 Gazetteer Files
Total area828.2 sq mi2025 Gazetteer Files
Population density?488 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$149,091American Community Survey 2020-2024 5-Year Estimates
Median home value$1,507,300American Community Survey 2020-2024 5-Year Estimates
Median age47.4American Community Survey 2020-2024 5-Year Estimates
Households103,018American Community Survey 2020-2024 5-Year Estimates
Housing units112,116American 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
+28
2,172 births, 2,144 deaths
Net migration
-2,026
More people moved out than moved in.

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

The 4 areas bordering Marin 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
Sonoma CountyCalifornia57 mi486,444
San Francisco CountyCalifornia19 mi826,079
Contra Costa CountyCalifornia12 mi1,170,070
Solano CountyCaliforniaa single point455,376

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

All 58 counties of California

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

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