California Counties by Population (2025)

There are 58 counties in California.

Not surprisingly, Los Angeles County is the largest county in the state, as well as the nation, with a huge population of 10,150,558 that continues to grow. The most recent census shows that its population has increased by 3.32% since the last census.

A number of other Californian counties also boast large populations, although they look small in comparison to Los Angeles County:

• San Diego County: 3,337,685 (growth rate of 7.8%)
• Orange County: 3,190,400 (growth rate of 6%)

California Counties with the Fewest Residents

The smallest county in California is Alpine County, with its population of just 1,120. This total represents a decrease of 4.7% since the last census count performed in 2010.

Other small counties include:

• Sierra County: 2,999 (growth rate of -7.4%)
• Modoc County: 8,859 (growth rate of -8.5%)
• Trinity County: 12,839 (growth rate of -4.1%)
• Del Norte County: 27,450 (growth rate of -6.3%)
• Siskiyou County: 43,511 (growth rate of -5.8%)

One smaller county, San Benito County, has increased its population by an impressive 6.85% since the last census and now has 59,335 residents.

California Counties with Rapid Growth

Alameda County, with its sizeable population of 1,653,236, has shown the largest population growth, with a substantial increase of 10.1% – this can perhaps be attributed to its proximity to San Francisco. Indeed, San Francisco County also has substantial population growth of 8.73% and 876,103 residents.

On the other hand, Lassen County has the highest negative growth, with its 31,000 residents representing a significant decrease of -10.7%.