County outline
Where Humboldt County is located
Area breakdown
Land accounts for 88.1% of Humboldt County’s measured area and water for 11.9%. Its combined area converts to 10,495.3 square kilometers or approximately 2,593,443 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 3,568.025 | 9,241.142 | 2,283,536 |
| Water | 484.23 | 1,254.15 | 309,907.2 |
| Total | 4,052.255 | 10,495.292 | 2,593,443.2 |
How Humboldt County compares
By original Census land area, Humboldt County ranks #14 of 58 in California and #142 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 2.323 times the California county-equivalent median of 1,535.7 square miles. It accounts for 2.3% of the combined county land area in the state.
See the complete California ranking · What counts as a county equivalent?
Population and density of Humboldt County
The Census Bureau estimates that 131,647 people lived in Humboldt County on July 1, 2025. That ranks #506 of 3,222 county equivalents nationally and #35 of 58 in California. Since the April 1, 2020 estimates base of 136,462, the population has declined by 4,815 (−3.5%), compared with −0.5% for California as a whole.
With 3,568 square miles of land, that is 37 people per square mile (14 per km²), placing Humboldt County #1,830 nationally for density and #42 in California. The median county equivalent has 47 people per square mile; the California median is 112. Put another way, there are about 17 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 136,298 | 135,070 | 134,979 | 133,956 | 132,324 | 131,647 |
| Change | — | −1,228 | −91 | −1,023 | −1,632 | −677 |
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 Humboldt County
7 incorporated places lie at least partly in Humboldt County. Together they are home to 62,374 people (47.4%); the other 69,273 (52.6%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Eureka city, with 25,304 residents in the county. Among places with at least 1,000 residents in 2020, Arcata city grew fastest since then (+1.1%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Eureka cityCounty seat | 25,304 | −4.7% | 9.567 |
| Arcata city | 19,047 | +1.1% | 9.416 |
| Fortuna city | 12,003 | −4.1% | 5.252 |
| Rio Dell city | 3,211 | −4.9% | 2.484 |
| Ferndale city | 1,348 | −3.9% | 1.206 |
| Blue Lake city | 1,144 | −5.8% | 0.618 |
| Trinidad city | 317 | −6.2% | 0.488 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Humboldt County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Humboldt County is a central county of the Eureka-Arcata, CA Micropolitan Statistical Area. Humboldt County is the area’s only county equivalent, so the micro area has the same 3,568 square miles of land. By combined land it ranks #40 of 542 micropolitan areas, and #13 by population.
ZIP codes
36 ZIP Code Tabulation Areas have land in Humboldt County; 35 of them have most of their land inside the county, and the others mainly cover neighboring areas.
955019550395511955149551995521955249552595526955289553695537955409554295545955469554795549955509555195552955539555495555955569555895559955609556295564955659556995570955719557395589
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 Humboldt County
Humboldt County shares a land border with 4 county equivalents. It has more land than 3 of them. The largest neighbor is Siskiyou County (6,278.8 mi²) and the smallest is Del Norte County (1,006.2 mi²). Together with its neighbors, Humboldt County forms a block of 17,539.1 mi² of land, of which it holds 20.3%.
| Bordering county equivalent | Land mi² | Size vs. Humboldt | Compare |
|---|---|---|---|
| Siskiyou County | 6,278.8 | 1.8× larger | Compare |
| Mendocino County | 3,506.8 | about the same | Compare |
| Trinity County | 3,179.3 | 1.1× smaller | Compare |
| Del Norte County | 1,006.2 | 3.5× smaller | Compare |
How big is Humboldt County compared with U.S. states?
Humboldt County has more land than 2 of the 50 states. It is about 1.8 times the land area of Delaware (1,948.6 mi²), while Connecticut, the next larger state, has 1.4 times as much land (4,842.5 mi²). California’s county land could hold about 44 areas the size of Humboldt County.
Another way to picture it: the same land area would fill a square about 59.7 miles (96.1 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 Humboldt County?
Humboldt County has more land than 3,080 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 Humboldt County at #129 nationally by total area, 13 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 11.9%, compared with a national county-equivalent median of 1.2% — 10.8 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 Humboldt County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #141 | Esmeralda County, Nevada | 3,581.9 | Compare |
| #142 | Humboldt County, California | 3,568 | This county |
| #143 | Mendocino County, California | 3,506.8 | 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 40.706655, -123.926176. 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: 9,241,141,630 m²; AWATER: 1,254,149,679 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 Humboldt County?
Humboldt County, California has 3,568 square miles (9,241.1 km²) of land and 484.2 square miles of water, for a total area of 4,052.3 square miles. It ranks #142 of 3,222 U.S. county equivalents by land area.
Is Humboldt County the largest county in California?
No. Humboldt County ranks #14 of 58 in California by land area. The largest is San Bernardino County, with 20,068.4 square miles of land.
What counties border Humboldt County?
Humboldt County shares a land border with Trinity County, Del Norte County, Mendocino County, and Siskiyou County.
What is the population of Humboldt County?
The Census Bureau estimates Humboldt County had 131,647 residents on July 1, 2025, ranking #506 of 3,222 county equivalents. That is 37 people per square mile of land.
What is the county seat of Humboldt County?
The county seat of Humboldt County is Eureka.
What cities and towns are in Humboldt County?
Humboldt County has 7 incorporated places. The most populous five are Eureka city, Arcata city, Fortuna city, Rio Dell city, and Ferndale city; 69,273 residents live outside any incorporated place.
Is Humboldt County part of a metropolitan area?
Yes. It is a central county of the Eureka-Arcata, CA Micropolitan Statistical Area.
How many ZIP codes are in Humboldt County?
36 ZIP Code Tabulation Areas have land in Humboldt County, and 35 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Humboldt County compare with U.S. states?
It has more land than 2 of the 50 states, including Delaware (1,948.6 square miles of land).
How many acres of land are in Humboldt County?
The land measurement converts to approximately 2,283,536 acres. Including water, total area is approximately 2,593,443 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.