San Mateo County, California: New American county. In 2024, voted D+50%. Democratic peak: D+58 in 2020.
Key facts
- 2024 presidential margin
- D+50MIT Election Lab
- Political typology
- New AmericanAkashic typology
- Population
- 742,3402024 5-year
- Median household income
- $158,8552024 5-year
- White (non-Hispanic)
- 37.8%2024 5-year
- Black
- 2.1%2024 5-year
- Hispanic / Latino
- 24.9%2024 5-year
- Peak Democratic margin
- D+58 in 2020MIT Election Lab
- Peak Republican margin
- R+51 in 1920MIT Election Lab
- Most similar
- Marin County, CA · similarity 1.00
2024 results by precinct
2024 precinct map of San Mateo CountyPrecinct-level 2024 presidential results for San Mateo County, with each precinct boundary colored by Democratic-vs-Republican margin.
—
Margin—
Turnout—
Harris +50Trump +50
Real precinct boundaries. Hover for vote totals.
presidential history
Presidential margin, 1876–2024
Democratic minus Republican, by election
| Year | Margin (D minus R) |
|---|---|
| 1876 | −11.2% |
| 1880 | −2.7% |
| 1884 | −11.6% |
| 1888 | −6.7% |
| 1892 | −3.2% |
| 1896 | −23.6% |
| 1900 | −28.0% |
| 1904 | −41.3% |
| 1908 | −34.1% |
| 1912 | +46.5% |
| 1916 | −6.9% |
| 1920 | −51.4% |
| 1924 | −50.0% |
| 1928 | −18.9% |
| 1932 | +16.7% |
| 1936 | +32.6% |
| 1940 | +5.8% |
| 1944 | +1.5% |
| 1948 | −17.0% |
| 1952 | −26.6% |
| 1956 | −22.2% |
| 1960 | −3.7% |
| 1964 | +28.8% |
| 1968 | +3.5% |
| 1972 | −10.0% |
| 1976 | −6.2% |
| 1980 | −12.2% |
| 1984 | −5.0% |
| 1988 | +12.8% |
| 1992 | +26.8% |
| 1996 | +31.3% |
| 2000 | +33.3% |
| 2004 | +40.2% |
| 2008 | +48.7% |
| 2012 | +46.7% |
| 2016 | +57.2% |
| 2020 | +57.7% |
| 2024 | +50.3% |
DemocraticRepublican
38 presidential elections
| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| D | 242,957 | 76,616 | 330,565 | ||
| D | 291,496 | 75,584 | 374,251 | ||
| D | 237,882 | 57,929 | 314,384 | ||
| D | 206,085 | 72,756 | 285,720 | ||
| D | 222,826 | 75,057 | 303,292 | ||
| D | 197,922 | 83,315 | 284,857 | ||
| D | 166,757 | 80,296 | 259,399 | ||
| D | 152,304 | 73,508 | 251,532 | ||
| D | 149,232 | 75,080 | 276,508 | ||
| D | 141,859 | 109,261 | 254,480 | ||
| R | 122,268 | 135,185 | 260,631 | ||
| R | 87,335 | 116,491 | 238,637 | ||
| R | 102,896 | 117,338 | 231,741 | ||
| R | 109,745 | 135,377 | 256,297 | ||
| D | 106,519 | 98,654 | 225,668 | ||
| D | 140,978 | 77,916 | 219,191 | ||
| R | 97,154 | 104,570 | 202,252 | ||
| R | 63,637 | 100,049 | 163,903 | ||
| R | 50,802 | 87,780 | 139,222 | ||
| R | 34,215 | 48,909 | 86,272 | ||
| D | 34,594 | 33,590 | 68,342 | ||
| D | 29,831 | 26,539 | 56,951 | ||
| D | 27,087 | 13,650 | 41,248 | ||
| D | 19,094 | 13,442 | 33,879 | ||
| R | 9,755 | 14,360 | 24,392 | ||
| R | 771 | 8,126 | 14,702 | ||
| R | 1,958 | 7,205 | 10,217 | ||
| R | 4,485 | 5,207 | 10,411 | ||
| O | 3,246 | 0 | 6,985 | ||
| R | 1,314 | 2,865 | 4,554 | ||
| R | 851 | 2,146 | 3,135 | ||
| R | 914 | 1,645 | 2,611 | ||
| R | 987 | 1,607 | 2,630 | ||
| R | 1,020 | 1,088 | 2,152 | ||
| R | 980 | 1,121 | 2,117 | ||
| R | 750 | 950 | 1,717 | ||
| R | 720 | 760 | 1,490 | ||
| R | 696 | 871 | 1,567 |
Demographics
2024 ACS
Race, ethnicity, and ancestry
Click any group to see the ancestries typically reported within it.
Irish
6.6%
German
6.0%
English
6.0%
Italian
5.0%
American
2.8%
French
1.7%
Scottish
1.3%
African American
1.7%
Multiple ancestry combinations reported; no single grouping above 1%.
American Indian, Alaska Native, Native Hawaiian, and Pacific Islander combined.
Source · American Community Survey 5-year estimates, 2024 release. Hispanic/Latino is an ethnicity that overlaps the race categories, so these shares can total more than 100%. Ancestry is a self-reported, multiple-response item; ancestry percentages do not sum to the parent race percentage.
2024 ACS
Age distribution by sex
Median age: 40.9 in this county, 39.1 nationally
Male
Age
Female
85+
75–84
65–74
55–64
45–54
35–44
25–34
18–24
5–17
<5
Source · American Community Survey 5-year estimates, 2024 release.
2024 ACS
Median household income
Inflation-adjusted dollars
$158,855
San Mateo County ranks in the top 0.5% of US counties.
San Mateo County$158,855
California$99,122
United States$80,734
San Mateo County ranks in the top 0.5% of US counties by median household income.
Source · American Community Survey 5-year estimates, 2024 release.
2024 ACS
Poverty rate
All persons below federal poverty line
6.7%
Child poverty is below the national average.
Children under 186.2%
Working age (18–64)6.4%
Seniors (65+)10.7%
Source · American Community Survey 5-year estimates, 2024 release.
2024 ACS
Language at home
Population aged 5 and older
54.2%
speak English only
Asian & Pacific Islander19.9%
Spanish17.6%
Other Indo-European7.0%
Other languages1.2%
Source · ACS 5-year estimates, 2024.
2020 religion census
Religious adherents
Adherents per capita by tradition
Source · 2020 US Religion Census. Remaining 66.2% of residents not counted as adherents by any reporting body.
San Mateo County sits between San Francisco and Silicon Valley, combining high housing costs and a highly educated workforce with some of the most consistent Democratic margins on the California coast.
San Mateo County has leaned Democratic in recent presidential elections, reaching a Democratic margin of fifty-eight points in 2020. Between 2020 and 2024 it moved seven points toward the Republican candidate — part of the sharpest rightward shift recorded among any group of places in the country.
Its demographics describe the shift: a 38% non-Hispanic-white share, a median household income of $158,855, and a population of 742,340. The county's voting pattern over the last decade is most similar to that of Marin County and Richmond city.
Most similar counties
Compare two places, side by side
Twelve curated comparisons line up election history, demographics, and the divergence story for two places at a glance. Browse all comparisons →
Cite this page
All citations released under CC BY 4.0. Attribution: Akashic Intelligence.
San Mateo County, California. Akashic. https://akashic.app/county/06081/. Accessed May 20, 2026. License: CC BY 4.0.
License: CC BY 4.0
More in California
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Frequently asked questions
How did San Mateo County, California vote in 2024?
In 2024, San Mateo County, California voted Democratic by 50.3 points (D+50), carried by the Democratic candidate. Out of 330,565 votes cast, 242,957 went Democratic and 76,616 went Republican.
What is San Mateo County, California's political typology?
Akashic places San Mateo County, California in the "New American" typology — Communities where a large share of households speak a language other than English — multilingual, Democratic-leaning overall, yet the hardest-swinging bloc toward the Republican Party in 2024. The typology is a data-driven cluster built from vote share, vote swing, race and ethnicity, income, language spoken at home, religion, and ancestry. Across 38 elections in the dataset, the county has voted Democratic 16 times, Republican 21 times, and other 1 times.
When did San Mateo County, California last vote Republican?
The most recent presidential election in which San Mateo County, California voted Republican was 1984.
How many people live in San Mateo County, California?
San Mateo County, California has a population of 742,340 according to the 2024 American Community Survey 5-year estimates from the US Census Bureau.
What is the median household income in San Mateo County, California?
Median household income in San Mateo County, California is $158,855 — above the national median of $80,734. The California state median is $99,122.
What is the political history of San Mateo County, California?
Akashic tracks 38 presidential elections in San Mateo County, California from 1876 to 2024. Of those, 16 went Democratic and 21 went Republican. The county's typology — "New American" — captures where that record, its demographics, and its recent swing place it among American communities.