
San Mateo County
- State:
- California
- County Seat:
- Redwood City
San Mateo County's estimated 2025 population is 721,201 with a growth rate of -0.36% in the past year according to the most recent United States census data. San Mateo County is the 15th largest county in California. The 2010 population was 719,948 and has seen a growth of 0.17% since that time.