San Mateo County, California
Voting in San Mateo County, California? Find registration links, ID rules, early and absentee voting options and your sample ballot here. Home to about 743,000 people, San Mateo County ranks 15th in population among California's 58 counties. In California, each county elections office, often called the registrar of voters, handles registration, mails ballots and publishes the county voter information guide with your sample ballot.
Next Election
March 7, 2028
Voter Portal
Register Online
What's On My Ballot?
ID Requirements
Absentee / Early Voting
Registration Deadline
Register online or by mail at least 15 days before an election; conditional same-day registration is available after the deadline.
Why Voting Matters
In San Mateo County, the people who show up to vote decide who represents everyone. The next election for San Mateo County voters is California's presidential primary on March 7, 2028; local elections can come sooner, so check your local election office. Many San Mateo County jobs are in media and technology and professional and technical services, so decisions about broadband and broadband and innovation hit close to home.
About 331,000 people voted for president in San Mateo County in 2024 (down about 12% from 374,000 in 2020). That equals roughly 55% of the county's estimated 602,000 adults, above the statewide rate of about 51%.
Around 272,000 adults here did not vote for president. Some aren't eligible, yet the rest are untapped power: one more voter in every 20 of them would mean about 13,600 extra San Mateo County ballots, enough to change the result in many close contests.
Spread over about 449 square miles, San Mateo County averages roughly 1,656 residents per square mile, one of the denser places in California. The county is home to about 1.9% of California's population.
ZIP codes in or partly in San Mateo County include 94002, 94005, 94010, 94011, 94014, 94015, 94017 and 94018, plus 32 more. Confirm your registration, read through your sample ballot before Election Day, and choose whether you will vote early, by mail or in person. Invite someone you know in San Mateo County to join you.
Voter Assistance Resources
Questions about voting in San Mateo County? In California, each county elections office, often called the registrar of voters, handles registration, mails ballots and publishes the county voter information guide with your sample ballot. For registration, polling places, early voting and absentee ballots, contact the San Mateo County elections office (registrar of voters).
Statewide directory, California Secretary of State's county elections offices list:
https://www.sos.ca.gov/elections/voting-resources/county-elections-offices
See your sample ballot. California county elections offices (your county mails and posts your sample ballot):
https://www.sos.ca.gov/elections/voting-resources/county-elections-offices
You can also preview a personalized ballot at Vote411.org.
To ask a question or report a problem at the polls, call or text Election Protection at 866-OUR-VOTE (866-687-8683), a free nonpartisan hotline. For help in Spanish call 888-VE-Y-VOTA (888-839-8682); for Asian languages call 888-API-VOTE (888-274-8683).
Voters with disabilities in San Mateo County can ask for an accessible voting machine, curbside voting where offered, and help from a person of their choice. If you run into barriers, contact Disability Rights California, California's Protection and Advocacy agency, at (888) 569-7955. VoteRiders (844-338-8743) offers free help with voter ID.
Need a ride? Many local transit agencies and ride services offer free or discounted rides to the polls on Election Day, so check what is available before the next election. See our California voter page for statewide options. Details can change, so confirm with the official election office.
Military and overseas voters can get help from the Federal Voting Assistance Program at 1-800-438-VOTE (8683) or fvap.gov.
Sign up to be an election worker
Election workers (often called poll workers) keep voting running smoothly in San Mateo County. Most are paid for their time, get free training, and help their neighbors cast their ballots. You can work a full day, a shorter shift, or help before Election Day. County and municipal election offices recruit and train their own workers, and the EAC's Help America Vote page links to yours. Find out how to sign up:
https://www.eac.gov/help-america-vote
Take the Next Step
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