Data as of October 18, 2026 · refreshed automatically from the official California voter file
San Mateo County, CA has 448,211 active registered voters — 14.7% Republican, 54.8% Democratic, and 24.6% with no party affiliation, as of October 2026.
Party registration
Most reliable-voting precincts
| # | Precinct | Active voters | Supervoters | Supervoter % |
|---|---|---|---|---|
| 1 | 39003-1 | 477 | 364 | 76.31% |
| 2 | 33026 | 680 | 512 | 75.29% |
| 3 | 37201 | 422 | 316 | 74.88% |
| 4 | 37205 | 786 | 583 | 74.17% |
| 5 | 37341 | 455 | 337 | 74.07% |
| 6 | 37206 | 561 | 415 | 73.98% |
| 7 | 37111 | 658 | 481 | 73.1% |
| 8 | 33027 | 721 | 526 | 72.95% |
| 9 | 46048 | 792 | 577 | 72.85% |
| 10 | 35055 | 541 | 393 | 72.64% |
Supervoters are active registered voters who cast a ballot in at least 3 of the last 4 November general elections (2018–2024). Percentages are precinct totals from the official state voter file — no individual voter information is shown. Precincts with fewer than 400 active voters are excluded.
How San Mateo County voted for president
Election results are public records.
San Mateo County at a glance.
San Mateo County had an estimated 742,893 residents in July 2024, the 15th most populous of California's 58 counties, down 2.8% since the 2020 census. Of those, 602,707 are 18 or older, the voting-age population, and 18.8% are 65 or older. Its 448,211 active registered voters equal about 74.4% of that voting-age population.
It covers 449 square miles of land (1,656 people per square mile), and 8.2% of residents live outside any incorporated city or town. The largest cities and towns are San Mateo (103,006), Daly City (101,418), Redwood City (82,982), South San Francisco (64,660) and San Bruno (42,035). The American Community Survey (2020-2024) puts it at a median age of 40.9, a median household income of $158,855, 53.7% of adults 25 and older holding a bachelor's degree or higher and 58.5% of occupied homes owned by the people living in them.
In 2024, 330,510 votes were cast for president, about 54.8% of the voting-age population; the Democratic ticket took 73.5% and the Republican ticket 23.2%. The two-party margin moved from D+48.8 in 2008 to D+50.3 in 2024.
- Population (2024 estimate)
- 742,893
- Population (2020 census base)
- 764,659
- Voting-age population (18+)
- 602,707
- Active voters per 100 adults
- 74.4
- Residents 65 and older
- 18.8%
- People per square mile
- 1,656
- Living outside incorporated places
- 8.2%
- Land area
- 449 sq mi
- Median age
- 40.9
- Median household income
- $158,855
- Adults 25+ with a bachelor's degree
- 53.7%
- Owner-occupied homes
- 58.5%
Largest cities and towns
- San Mateo 103,006
- Daly City 101,418
- Redwood City 82,982
- South San Francisco 64,660
- San Bruno 42,035
Presidential vote, 2008–2024
| Year | Democratic | Republican | Margin | Votes cast |
|---|---|---|---|---|
| 2024 | 73.5% | 23.2% | D+50.3 | 330,510 |
| 2020 | 77.9% | 20.2% | D+57.7 | 374,138 |
| 2016 | 76.4% | 18.7% | D+57.7 | 287,499 |
| 2012 | 71.3% | 26.6% | D+44.7 | 211,814 |
| 2008 | 73.5% | 24.7% | D+48.8 | 303,292 |
Sources: U.S. Census Bureau Vintage 2024 population estimates and 2024 Gazetteer; American Community Survey 2020–2024 5-year estimates; certified county presidential returns. Growth, density and turnout are simple arithmetic on those figures.
Running in San Mateo County?
The voter file is loaded. Create your campaign and start canvassing in minutes.
Start free in San Mateo CountyAlso see: Motion51 in California · Pricing