The Population of Counties in California?

Last updated on December 19th, 2023 at 10:25 am


The State of California holds several records in the United States: 1) it has the largest number of people living in it, 2) it has the largest Gross State Product (GSP). GSP is equivalent to GDP, and 3) it is the third largest U.S. state by land area.

California has 58 counties. In this article, we’re taking a look at the population of counties in California and the demographics of residents in each of the counties.

Does population really matter?

Population and demographics are very important data the government of the United States doesn’t play with.


It helps in knowing the age and sex of the people, persons under 18, people over 65 years, and the race of the residents among other actionable information that guides the government in drawing up policies that will impact the people.

What’s the most populated California County?

The largest county in California by population is Los Angeles County with 9,829,544 according to the July 1, 2021 population estimates which is obtained from the data page of the United States Census Bureau.

A closer look shows Los Angeles County had 10,014,009 residents as of 2020 population, showing -1.8% when compared with 2021.

The largest California County by population has its seat in Los Angeles, a city known for its opulence and home to Hollywood and entertainment. It is also adjudged to be one of the most expensive U.S. cities to buy a home and live in.

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By age, 14.6% of residents of Los Angeles County are 65 years old and above; 21.1% of the population are persons under 18 years old.

Using race and origin, the county is predominately white (70.2 per cent) while black or African American take 9 per cent; American Indians are just 1.5 per cent.

The second largest County by population in California is San Diego County with 3,286,069 people. Created in 1850, the County has its seat in San Diego City.

By income and poverty, the median household income in San Diego County is $82,426; per capita income is put at $39,737. 9.5% live in poverty.

By age and sex, 49.3 per cent is female; 14.9% are persons 65 years old and above while 21.3% are persons under 18 years old.

Coming in the third position is Orange County with 3,167,809 population figures and has its seat in Santa Ana. This is followed by Riverside County and San Bernardino County with 2,458,395 and 2,194,710 respectively in the fourth and fifth positions. But San Bernardino is the largest California County by land area.

What are the smallest Counties in California?

Alpine County, Sierra County, Modoc County, Trinity County, and Mono County are the smallest Counties in the state of California.

Alpine County has just 1,235 population figure, making it the smallest California county. The County was carved out of Amador, El Dorado, Calaveras, Mono and Tuolumne counties in 1864 with its headquarters sitting in its largest community Markleeville.

Sierra County is the second smallest with 3,283 residents, according to the 2021 figure from U.S. Census Bureau.

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By demography, persons under 18 years constitute 16.8% of the population in Sierra County; 30.4% of the population are residents who are 65-year-old and above while under 5 years make up 4.3% of the population.

In the far northeast of California is Modoc County which is the third smallest county in the state with 8,661 people as of the 2021 estimates.

Trinity County and Mono County are fourth and fifth with 16,060 and 13,247 estimates respectively in terms of population figures.

As per 2021 estimates, California has 39,237,836 people making the state the largest by population among the 50 U.S. states

The table below shows the 58 Counties in California by population. The population data are from the 2021 U.S Census Bureau.

County2021 Estimates2020 Population
Los Angeles County9,829,54410,014,009
San Diego County3,286,0693,298,634
Orange County 3,167,8093,186,989
Riverside County2,458,3952,418,185
San Bernardino County2,194,7102,181,654
Santa Clara County1,885,5081,936,259
Alameda County1,648,5561,682,353
Sacramento County1,588,9211,585,055
Contra Costa County1,161,4131,165,927
Fresno County1,013,5811,008,654
Kern County917,673909,235
San Francisco County815,201873,965
Ventura County839,784843,843
San Joaquin County789,410779,233
San Mateo County737,888764,442
Stanislaus County552,999552,878
Sonoma County485,887488,863
Tulare County477,054473,117
Solano County451,716453,491
Santa Barbara County446,475448,229
Monterey County437,325439,035
Placer County412,300404,739
Merced County286,461281,202
San Luis Obispo County283,159282,424
Santa Cruz County267,792270,861
Marin County260,206262,321
Yolo County216,986216,403
El Dorado County193,221191,185
Butte County208,309211,632
Shasta County182,139182,155
Imperial County179,851179,702
Madera County159,410156,255
Kings County153,443152,486
Napa County136,207138,019
Humboldt County136,310136,463
Nevada County103,487102,241
Sutter County99,06399,633
Mendocino County91,30591,601
Yuba County83,42181,575
Tehama County65,49865,829
San Benito County66,67764,209
Lake County68,76668,163
Tuolumne County55,81055,620
Calaveras County46,22145,292
Siskiyou County44,11844,076
Amador County41,25940,474
Lassen County33,15932,730
Glenn County28,80528,917
Del Norte County28,10027,743
Colusa County21,91721,839
Plumas County19,91519,790
Inyo County18,97019,016
Mariposa County17,14717,131
Mono County13,24713,195
Trinity County16,06016,112
Modoc County8,6618,700
Sierra County3,2833,236
Alpine County1,2351,204
This population figure is based on 2020 census and 2021 estimates by Census Bureau, United States

A Decline in California Population

The population of each of the counties in California in the table above has evidently shown that there is a decline in California’s population. So, what’s responsible for the decline?

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While California remains the most populated state in the U.S., the state’s population shrunk by 182,083 residents in 2020. In 2021, it lost another 117,552 residents. A lot of factors are responsible for the decline.

Chief among them is the migration of residents out of the CA due to the high cost of living or affordability. California does rank well if affordability is used as a measure. For instance, an official figure put the number of residents who left the state at 275,000 in 2021.

In 2020, about 180,000 people left before the pandemic, which shows that the number of people that left increased in 2021. The trend isn’t a new phenomenon due to the cost of living in CA’s big cities like Los Angeles, San Francisco, and San Diego among other expensive cities in the state. People leave California for economic reasons, according to the Guardian of UK, to find a better place where their income can accommodate their expenses.


California’s population is 39,237,836 shared across all the 58 counties in the most populous U.S. state.

Los Angeles County is the largest California County by population while Alpine County is the smallest county.



  • Opeyemi Quadri

    Ope is a finance writer and researcher with 10+ years of experience in content creation. His interests cut across decentralized finance, investment, foreign exchange, government policies and politics.

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