Marin County area

Population and density of Marin County

The Census Bureau estimates that 253,694 people lived in Marin County on July 1, 2025. That ranks #292 of 3,222 county equivalents nationally and #26 of 58 in California. Since the April 1, 2020 estimates base of 262,312, the population has declined by 8,618 (−3.3%), compared with −0.5% for California as a whole.

With 520.1 square miles of land, that is 488 people per square mile (188 per km²), placing Marin County #342 nationally for density and #13 in California. The median county equivalent has 47 people per square mile; the California median is 112. Put another way, there are about 1.3 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in Marin County

11 incorporated places lie at least partly in Marin County. Together they are home to 187,947 people (74.1%); the other 65,747 (25.9%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is San Rafael city, with 59,410 residents in the county. By land, Novato city is the largest at 27.4 mi².

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Marin County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Marin County is a central county of the San Francisco-Oakland-Fremont, CA Metropolitan Statistical Area, in the San Rafael, CA metropolitan division. Its 5 county equivalents have 4,630,041 residents on 2,469.8 square miles of land; Marin County accounts for 21.1% of the land and 5.5% of the residents. By combined land it ranks #133 of 393 metropolitan areas, and #13 by population. It belongs to the San Jose-San Francisco-Oakland, CA Combined Statistical Area.

ZIP codes

29 ZIP Code Tabulation Areas have land in Marin County, and each lies mostly inside the county.

9490194903949049492094924949259492994930949339493794938949399494094941949459494694947949499495094952949569495794960949639496494965949709497194973

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Marin County

Marin County shares a land border with 2 county equivalents. It has more land than 1 of them. The largest neighbor is Sonoma County (1,575.3 mi²) and the smallest is San Francisco County (46.7 mi²). Together with its neighbors, Marin County forms a block of 2,142.2 mi² of land, of which it holds 24.3%.

How big is Marin County compared with U.S. states?

Marin County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2 times as much. California’s county land could hold about 300 areas the size of Marin County.

Another way to picture it: the same land area would fill a square about 22.8 miles (36.7 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about Marin County?

Marin County has more land than 1,218 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places Marin County at #1,121 nationally by total area, 883 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.

Its water share is 37.2%, compared with a national county-equivalent median of 1.2% — 36 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside Marin County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.