California Population By County in 2021 (ACS-5Yrs)

Updated on February 28, 2025.

Based on the US Census ACS-5Yrs estimates, in 2021, the total population of California was 39.46M. Among all California counties, Los Angeles was the most populated county (10.02M), followed by San Diego (3.30M), and then Orange (3.18M).

On the other hand, the least populated counties were: Alpine (1.34K), Sierra (3.08K), and Modoc (8.72K).

The chart and table below shows the population of each county and the percentage of California population in each county.

You can see similar information for other states and by state for the United States.

California Population By County in 2021
California Population By County in 2021
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County Population % of State Population
Alameda 1673133 4.24
Alpine 1344 0.00
Amador 40095 0.10
Butte 217884 0.55
Calaveras 45349 0.12
Colusa 21780 0.06
Contra Costa 1161643 2.94
Del Norte 27655 0.07
El Dorado 190568 0.48
Fresno 1003150 2.54
Glenn 28675 0.07
Humboldt 137014 0.35
Imperial 180051 0.46
Inyo 18804 0.05
Kern 905644 2.30
Kings 151887 0.39
Lake 67749 0.17
Lassen 32949 0.08
Los Angeles 10019635 25.40
Madera 156304 0.40
Marin 262387 0.67
Mariposa 17225 0.04
Mendocino 91534 0.23
Merced 279150 0.71
Modoc 8723 0.02
Mono 13291 0.03
Monterey 438953 1.11
Napa 138795 0.35
Nevada 102090 0.26
Orange 3182923 8.07
Placer 400330 1.01
Plumas 19631 0.05
Riverside 2409331 6.11
Sacramento 1571767 3.98
San Benito 63329 0.16
San Bernardino 2171071 5.50
San Diego 3296317 8.36
San Francisco 865933 2.19
San Joaquin 771406 1.96
San Luis Obispo 282771 0.72
San Mateo 762488 1.93
Santa Barbara 447651 1.14
Santa Clara 1932022 4.90
Santa Cruz 272138 0.69
Shasta 181935 0.46
Sierra 3079 0.01
Siskiyou 44151 0.11
Solano 451432 1.14
Sonoma 492498 1.25
Stanislaus 550842 1.40
Sutter 99080 0.25
Tehama 65345 0.17
Trinity 15818 0.04
Tulare 470999 1.19
Tuolumne 55243 0.14
Ventura 845255 2.14
Yolo 216703 0.55
Yuba 80404 0.20