County outline
Where Sonoma County is located
Area breakdown
Land accounts for 89.1% of Sonoma County’s measured area and water for 10.9%. Its combined area converts to 4,577.4 square kilometers or approximately 1,131,099 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 1,575.337 | 4,080.104 | 1,008,215.7 |
| Water | 192.005 | 497.291 | 122,883.2 |
| Total | 1,767.342 | 4,577.395 | 1,131,098.9 |
How Sonoma County compares
By original Census land area, Sonoma County ranks #29 of 58 in California and #385 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 1.026 times the California county-equivalent median of 1,535.7 square miles. It accounts for 1% of the combined county land area in the state.
See the complete California ranking · What counts as a county equivalent?
Population and density of Sonoma County
The Census Bureau estimates that 486,444 people lived in Sonoma County on July 1, 2025. That ranks #152 of 3,222 county equivalents nationally and #17 of 58 in California. Since the April 1, 2020 estimates base of 488,860, the population has declined by 2,416 (−0.5%), compared with −0.5% for California as a whole.
With 1,575.3 square miles of land, that is 309 people per square mile (119 per km²), placing Sonoma County #497 nationally for density and #18 in California. The median county equivalent has 47 people per square mile; the California median is 112. Put another way, there are about 2.1 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 488,514 | 484,827 | 483,236 | 483,405 | 485,363 | 486,444 |
| Change | — | −3,687 | −1,591 | +169 | +1,958 | +1,081 |
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 Sonoma County
9 incorporated places lie at least partly in Sonoma County. Together they are home to 355,089 people (73%); the other 131,355 (27%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Santa Rosa city, with 179,437 residents in the county. Among places with at least 1,000 residents in 2020, Rohnert Park city grew fastest since then (+0.9%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Santa Rosa cityCounty seat | 179,437 | +0.8% | 42.6 |
| Petaluma city | 59,688 | −0.2% | 14.4 |
| Rohnert Park city | 44,811 | +0.9% | 7.286 |
| Windsor town | 25,864 | −1.9% | 7.436 |
| Healdsburg city | 11,172 | −1.6% | 4.42 |
| Sonoma city | 10,537 | −1.8% | 2.744 |
| Cloverdale city | 8,701 | −3.4% | 3.363 |
| Sebastopol city | 7,532 | −0.9% | 1.882 |
| Cotati city | 7,347 | −3.4% | 1.874 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Sonoma County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Sonoma County is a central county of the Santa Rosa-Petaluma, CA Metropolitan Statistical Area. Sonoma County is the area’s only county equivalent, so the metro area has the same 1,575.3 square miles of land. By combined land it ranks #212 of 393 metropolitan areas, and #114 by population.
ZIP codes
40 ZIP Code Tabulation Areas have land in Sonoma County; 38 of them have most of their land inside the county, and the others mainly cover neighboring areas.
94515945749492294923949289493194951949529495494972954019540395404954059540795409954129541995421954259543095431954369543995441954429544495446954489545095452954629546595471954729547695480954869549295497
ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.
Counties bordering Sonoma County
Sonoma County shares a land border with 5 county equivalents. It has more land than 4 of them. The largest neighbor is Mendocino County (3,506.8 mi²) and the smallest is Marin County (520.1 mi²). Together with its neighbors, Sonoma County forms a block of 8,431.1 mi² of land, of which it holds 18.7%.
| Bordering county equivalent | Land mi² | Size vs. Sonoma | Compare |
|---|---|---|---|
| Mendocino County | 3,506.8 | 2.2× larger | Compare |
| Lake County | 1,255.1 | 1.3× smaller | Compare |
| Solano County | 821.7 | 1.9× smaller | Compare |
| Napa County | 752 | 2.1× smaller | Compare |
| Marin County | 520.1 | 3× smaller | Compare |
How big is Sonoma County compared with U.S. states?
Sonoma County has more land than 1 of the 50 states. It is about 1.5 times the land area of Rhode Island (1,033.9 mi²), while Delaware, the next larger state, has 1.2 times as much land (1,948.6 mi²). California’s county land could hold about 99 areas the size of Sonoma County.
Another way to picture it: the same land area would fill a square about 39.7 miles (63.9 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 Sonoma County?
Sonoma County has more land than 2,837 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 Sonoma County at #381 nationally by total area, 4 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 10.9%, compared with a national county-equivalent median of 1.2% — 9.7 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 Sonoma County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #384 | Hancock County, Maine | 1,587.2 | Compare |
| #385 | Sonoma County, California | 1,575.3 | This county |
| #386 | Hidalgo County, Texas | 1,571.2 | Compare |
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.
Representative coordinates
The Census internal point is 38.521700, -122.916421. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 4,080,103,571 m²; AWATER: 497,291,850 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is Sonoma County?
Sonoma County, California has 1,575.3 square miles (4,080.1 km²) of land and 192 square miles of water, for a total area of 1,767.3 square miles. It ranks #385 of 3,222 U.S. county equivalents by land area.
Is Sonoma County the largest county in California?
No. Sonoma County ranks #29 of 58 in California by land area. The largest is San Bernardino County, with 20,068.4 square miles of land.
What counties border Sonoma County?
Sonoma County shares a land border with Napa County, Mendocino County, Marin County, Lake County, and Solano County.
What is the population of Sonoma County?
The Census Bureau estimates Sonoma County had 486,444 residents on July 1, 2025, ranking #152 of 3,222 county equivalents. That is 309 people per square mile of land.
What is the county seat of Sonoma County?
The county seat of Sonoma County is Santa Rosa.
What cities and towns are in Sonoma County?
Sonoma County has 9 incorporated places. The most populous five are Santa Rosa city, Petaluma city, Rohnert Park city, Windsor town, and Healdsburg city; 131,355 residents live outside any incorporated place.
Is Sonoma County part of a metropolitan area?
Yes. It is a central county of the Santa Rosa-Petaluma, CA Metropolitan Statistical Area.
How many ZIP codes are in Sonoma County?
40 ZIP Code Tabulation Areas have land in Sonoma County, and 38 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Sonoma County compare with U.S. states?
It has more land than 1 of the 50 states, including Rhode Island (1,033.9 square miles of land).
How many acres of land are in Sonoma County?
The land measurement converts to approximately 1,008,216 acres. Including water, total area is approximately 1,131,099 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.