County outline
Where Solano County is located
Area breakdown
Land accounts for 90.7% of Solano County’s measured area and water for 9.3%. Its combined area converts to 2,346.9 square kilometers or approximately 579,932 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 821.742 | 2,128.302 | 525,914.9 |
| Water | 84.402 | 218.6 | 54,017.3 |
| Total | 906.144 | 2,346.902 | 579,932.2 |
How Solano County compares
By original Census land area, Solano County ranks #46 of 58 in California and #1031 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.535 times the California county-equivalent median of 1,535.7 square miles. It accounts for 0.5% of the combined county land area in the state.
See the complete California ranking · What counts as a county equivalent?
Population and density of Solano County
The Census Bureau estimates that 455,376 people lived in Solano County on July 1, 2025. That ranks #165 of 3,222 county equivalents nationally and #19 of 58 in California. Since the April 1, 2020 estimates base of 453,556, the population has grown by 1,820 (+0.4%), compared with −0.5% for California as a whole.
With 821.7 square miles of land, that is 554 people per square mile (214 per km²), placing Solano County #313 nationally for density and #12 in California. The median county equivalent has 47 people per square mile; the California median is 112. Put another way, there are about 1.2 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 452,895 | 451,048 | 449,852 | 451,377 | 455,076 | 455,376 |
| Change | — | −1,847 | −1,196 | +1,525 | +3,699 | +300 |
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 Solano County
7 incorporated places lie at least partly in Solano County. Together they are home to 437,120 people (96%); the other 18,256 (4%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Vallejo city, with 123,287 residents in the county. The county seat, Fairfield city, has 122,489 residents. By land, Fairfield city is the largest at 41.6 mi². Among places with at least 1,000 residents in 2020, Dixon city grew fastest since then (+8.8%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Vallejo city | 123,287 | −2.2% | 30.4 |
| Fairfield cityCounty seat | 122,489 | +2.1% | 41.6 |
| Vacaville city | 103,850 | +1.4% | 29.9 |
| Suisun City city | 29,454 | −0.2% | 4.005 |
| Benicia city | 26,401 | −2.7% | 12.8 |
| Dixon city | 21,116 | +8.8% | 7.1 |
| Rio Vista city | 10,523 | +5% | 6.6 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Solano County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Solano County is a central county of the Vallejo, CA Metropolitan Statistical Area. Solano County is the area’s only county equivalent, so the metro area has the same 821.7 square miles of land. By combined land it ranks #302 of 393 metropolitan areas, and #121 by population. It belongs to the San Jose-San Francisco-Oakland, CA Combined Statistical Area.
ZIP codes
21 ZIP Code Tabulation Areas have land in Solano County; 15 of them have most of their land inside the county, and the others mainly cover neighboring areas.
945039451094512945339453494535945719458594589945909459194592956129561695618956209562595687956889569095694
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 Solano County
Solano County shares a land border with 5 county equivalents. It has more land than 2 of them. The largest neighbor is Sonoma County (1,575.3 mi²) and the smallest is Contra Costa County (716.9 mi²). Together with its neighbors, Solano County forms a block of 5,844.3 mi² of land, of which it holds 14.1%.
| Bordering county equivalent | Land mi² | Size vs. Solano | Compare |
|---|---|---|---|
| Sonoma County | 1,575.3 | 1.9× larger | Compare |
| Yolo County | 1,013 | 1.2× larger | Compare |
| Sacramento County | 965.4 | 1.2× larger | Compare |
| Napa County | 752 | 1.1× smaller | Compare |
| Contra Costa County | 716.9 | 1.1× smaller | Compare |
How big is Solano County compared with U.S. states?
Solano County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.3 times as much. California’s county land could hold about 190 areas the size of Solano County.
Another way to picture it: the same land area would fill a square about 28.7 miles (46.1 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 Solano County?
Solano County has more land than 2,191 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 Solano County at #944 nationally by total area, 87 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 9.3%, compared with a national county-equivalent median of 1.2% — 8.1 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 Solano County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1030 | Carter County, Oklahoma | 822.3 | Compare |
| #1031 | Solano County, California | 821.7 | This county |
| #1032 | Burnett County, Wisconsin | 821.6 | 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 38.267226, -121.939594. 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: 2,128,301,077 m²; AWATER: 218,600,179 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 Solano County?
Solano County, California has 821.7 square miles (2,128.3 km²) of land and 84.4 square miles of water, for a total area of 906.1 square miles. It ranks #1031 of 3,222 U.S. county equivalents by land area.
Is Solano County the largest county in California?
No. Solano County ranks #46 of 58 in California by land area. The largest is San Bernardino County, with 20,068.4 square miles of land.
What counties border Solano County?
Solano County shares a land border with Napa County, Yolo County, Sacramento County, Contra Costa County, and Sonoma County.
What is the population of Solano County?
The Census Bureau estimates Solano County had 455,376 residents on July 1, 2025, ranking #165 of 3,222 county equivalents. That is 554 people per square mile of land.
What is the county seat of Solano County?
The county seat of Solano County is Fairfield.
What cities and towns are in Solano County?
Solano County has 7 incorporated places. The most populous five are Vallejo city, Fairfield city, Vacaville city, Suisun City city, and Benicia city; 18,256 residents live outside any incorporated place.
Is Solano County part of a metropolitan area?
Yes. It is a central county of the Vallejo, CA Metropolitan Statistical Area.
How many ZIP codes are in Solano County?
21 ZIP Code Tabulation Areas have land in Solano County, and 15 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Solano County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.3 times as much land.
How many acres of land are in Solano County?
The land measurement converts to approximately 525,915 acres. Including water, total area is approximately 579,932 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.