742,893 people (2024 Census estimate, −2.6% since 2020)
449 square miles of land · 1,656 people per square mile
“Highest” and “lowest” are just order, not grades: a high rank for poverty or hazard losses means more of it. Each figure's source is in its section below.
36 active community water systems list San Mateo County in the area they serve, reporting 773,058 people served in all (a system that crosses county lines counts its whole population).
| CALIFORNIA WATER SERVICE - SAN MATEO buys surface water · private · CA4110008 | 103,536 served |
| CITY OF DALY CITY buys surface water · local government · CA4110013 | 102,593 served |
| CITY OF REDWOOD CITY buys surface water · local government · CA4110022 | 90,043 served |
| CALIFORNIA WATER SERVICE-S SAN FRANCISCO buys surface water · private · CA4110009 | 62,609 served |
| CALIFORNIA WATER SERVICE - BEAR GULCH surface water · private · CA4110006 | 60,382 served |
| CITY OF SAN BRUNO buys surface water · local government · CA4110023 | 42,631 served |
| NORTH COAST COUNTY WATER DIST buys surface water · local government · CA4110025 | 38,546 served |
| ESTERO MUNICIPAL IMPROVEMENT DISTRICT buys surface water · local government · CA4110021 | 36,556 served |
Source: U.S. EPA Safe Drinking Water Information System (SDWIS), active community systems, . Look up any system's violations and test results with EPA's search using its ID.
About 927 people were held in San Mateo County's jail, in Vera's latest figure (2025). In 2020 it was about 733.
Source: Vera Institute of Justice, Incarceration Trends (built from federal Bureau of Justice Statistics jail surveys). Counties without their own jail, or that share one, may show no figure.
24 school districts have their office in San Mateo County. School taxes are usually the largest part of a property tax bill.
Spent $279.8 million — $197.6 million to run schools, about $19,624 per student, plus $71.2 million on buildings and equipment. Money in: $191.4 million local (mostly property tax), $48.6 million state, $11.3 million federal. Long-term debt: $469.1 million.
Spent $305.4 million — $218.4 million to run schools, about $24,423 per student, plus $55.4 million on buildings and equipment. Money in: $259.8 million local (mostly property tax), $43.4 million state, $6.3 million federal. Long-term debt: $671.7 million.
Spent $259 million — $229.1 million to run schools, about $25,742 per student, plus $9.3 million on buildings and equipment. Money in: $253.2 million local (mostly property tax), $61.9 million state, $10.8 million federal. Long-term debt: $439.8 million.
Spent $165.3 million — $147.9 million to run schools, about $18,792 per student, plus $4.8 million on buildings and equipment. Money in: $147.5 million local (mostly property tax), $38.7 million state, $10.5 million federal. Long-term debt: $166.7 million.
Spent $166 million — $132.3 million to run schools, about $20,855 per student, plus $16.8 million on buildings and equipment. Money in: $117.1 million local (mostly property tax), $56.2 million state, $13.9 million federal. Long-term debt: $194 million.
Spent $106 million — $83.2 million to run schools, about $16,792 per student, plus $17.3 million on buildings and equipment. Money in: $16.3 million local (mostly property tax), $88.5 million state, $9.1 million federal. Long-term debt: $127.4 million.
Spent $62.7 million — $58.2 million to run schools, about $14,744 per student, plus $168,000 on buildings and equipment. Money in: $59.6 million local (mostly property tax), $12.5 million state, $2 million federal. Long-term debt: $124.2 million.
Spent $131.1 million — $84.3 million to run schools, about $21,712 per student, plus $32.2 million on buildings and equipment. Money in: $95.2 million local (mostly property tax), $19.9 million state, $5.7 million federal. Long-term debt: $336.6 million.
And 16 more.
Source: U.S. Census Bureau, 2023 Annual Survey of School System Finances. Districts are listed by the county of their main office; some serve neighboring counties too.
Source: County Health Rankings & Roadmaps 2025 (University of Wisconsin Population Health Institute), which gathers federal data (CDC, Census, and others); measures cover different recent years. Blank lines aren't reported for small counties.
Overall risk: Relatively High compared with other U.S. counties. FEMA estimates natural hazards cost San Mateo County about $740 million a year on average in buildings, crops and lives. Ability to bounce back (community resilience): Very High; social vulnerability: Relatively Low.
Source: FEMA National Risk Index (December 2025), expected annual loss. Ratings compare counties nationwide; they're estimates, not predictions.
361 bridges in San Mateo County: 100 in good condition, 224 fair, and 37 poor (10.2%). “Poor” means a main part — the deck, the beams, or the supports — is rated 4 or lower on the federal 0–9 scale. It doesn't mean unsafe to drive; unsafe bridges are closed.
| U.S. HIGHWAY 101 over CORDILLERAS CREEK · built 1930 | 195,000 vehicles a day |
| INTERSTATE 280 over SOUTHGATE AVENUE · built 1967 | 178,000 vehicles a day |
| STATE ROUTE 92 over SAN FRANCISCO BAY · built 1967 | 120,000 vehicles a day |
| US HIGHWAY 101 SB over CALTRAIN UP RR GRAND ONR · built 1948 | 98,000 vehicles a day |
| US HIGHWAY 101 NB over CALTRAIN UP RR GRAND ONR · built 1948 | 98,000 vehicles a day |
| SB STATE RTE 280 over SERRAMONTE BOULEVARD · built 1967 | 89,000 vehicles a day |
Source: Federal Highway Administration, National Bridge Inventory (2025 submission). Includes state, county and city bridges.
Federal grants paid for $159.8 million of work in San Mateo County in fiscal 2025, about $209 per resident — to the county, cities, schools, hospitals, nonprofits and others.
Source: USAspending.gov, grants by place of performance, fiscal 2025 (Oct. 2024 to Sept. 2025). Search it by county to see each award.
From Grants.gov: posted grants listing county governments as eligible, soonest deadline first; research-only and overseas programs left out; list updated 2026-10-13, refreshed weekly. 62 are open in all. Cities, towns, school districts and nonprofits have their own lists there.
General election: Tuesday, November 3, 2026. Ballots mailed; drop boxes open: 2026-10-05. Last day to register to vote: 2026-10-19. Early in-person voting: 2026-10-24 to 2026-11-03. Election Day: 2026-11-03. Last day for mailed ballots to arrive: 2026-11-10.
Source: California Secretary of State — Nov. 3, 2026 key dates · California Official Voter Information Guide — dates to remember · California Secretary of State — make a plan to vote
The budget, property tax rates, audits, local officials and offices for San Mateo County come from the county's own records, which we haven't gathered — not gathered, never hidden. See what a full county site looks like, or ask to have San Mateo County built: brayden.ozark@gmail.com.
More of California: the state government and every county in California.
Nearby counties: Alameda County (30 mi) · Santa Cruz County (34 mi) · Santa Clara County (40 mi) · Contra Costa County (42 mi) · San Francisco County (42 mi) · Marin County (48 mi).