Voter Registration

Access to voting is fundamental to ensuring equity. Voting allows people to have a say in government policy and processes. It is not perfect— there is a lot of interference between access to voting and implementation of the preferences of voters—but access is a necessary condition for democratic equity.
Eligible voters might not register to vote if they perceive barriers outweigh the benefits. Time and effort to register may be higher for those who do not have internet access at home; who live far from in-person registration facilities; have recently moved, frequently move, or do not have a steady address; recently became a citizen; require physical assistance to register or vote and/or accessible in-person registration facilities; or are in other special circumstances. This could mean that rural, poor, immigrant, migrant, those experiencing homelessness, disabled, and other already disadvantaged populations may be less likely to register to vote. Studies estimate that eliminating registration barriers raises voter turnout by 5 to 10%.[1]
The Current Population Survey,[2] sponsored by the U.S. Census Bureau and the U.S. Bureau of Labor Statistics, includes questions about voting and registration following each national election. According to the Current Population Survey, those who did not register to vote for the 2020 election reported that they did not register for many reasons. Reasons included were: not interested in the election or in politics (38.8%), they did not meet registration deadlines (10.6%), they were not eligible to vote (9.8%), they have a permanent illness or disability (4.9%), they believed their vote would not make a difference (4.7%), they did not know how or where to register (3.2%), they did not meet residency requirements (2.8%), they were concerned about the COVID-19 pandemic (2.3%), or they had difficulty with English (1.2%).[3] The Census reports how these explanations differ across race, age, and educational attainment across the country, but does not sample enough people in the Current Population Survey to allow for analysis in San Diego County.[4]
Additionally, people who would be disenfranchised in some states but can vote in California may not be aware that they are eligible to register in California, especially if they moved here from one of those states. For example, in California, most people convicted of a felony who have served their time are eligible to vote, but in some other states they are disenfranchised.
The map below shows the percent of adults 18 years of age and older in each ZIP code who were registered to vote as of September 1, 2021. The denominator includes some people who are not eligible to vote due to the difficulty in estimating sizes of the ineligible groups: non-citizens, people serving in state or federal prisons, and those found mentally incompetent are ineligible.[5] Although the consequence of including some ineligible people in the denominator is that these voter registration rates are slightly underestimates, comparing across ZIP codes is still useful. Differences not only help identify areas that may benefit from additional outreach, but also plainly show the proportion of adult residents who have the possibility of representation in elections.
Overall, 78.0% of the San Diego County population 18 years of age and older were registered to vote as of September 1, 2021. Downtown and surrounding areas had some of the lowest voter registration rates, while some ZIP codes in east and north county had higher rates. Some universities and military bases have their own ZIP codes; these ZIP codes are shown in grey. Voter registration data are not shown for these ZIP codes because it is likely that most of the population are university students and military members who are registered to vote at their home addresses elsewhere in the county or out of the county.
Although the County cannot address all the reasons that an eligible voter may not register, the County can continue to provide educational opportunities to potential voters, making registration (including pre-registration for first-time voters) easy and accessible, and working with community organizations that run registration drives in areas with low voter registration. The County of San Diego Registrar of Voters continually aims to improve access and ease of voting, often by leveraging strong partnerships with community-based organizations, community advisory committees, and trusted leaders in the community. In October 2021, the County of San Diego Board of Supervisors approved the County’s transition to a vote center model under the Voters Choice Act. The Election Administration Plan was finalized in March 2022 and outlines processes for future elections in San Diego County. Visit for more information about the Election Administration Plan and accurate information about upcoming elections.
Examining voter registration in San Diego County is limited by data availability. Voters in California are not required to report their race when registering to vote, resulting in a large amount of missing data that may bias registration rates that are disaggregated by race. Determining accurate estimates of the eligible population is difficult at the county level, although this may be explored for future reports. Additionally, voter registration alone does not fully reflect equity issues in all voting stages.

Data Information
Data Source: Voter registration data were obtained from the Registrar of Voters, data as of September 1, 2021.
  • Population data is the 2021 SANDAG population estimates (prepared Sep. 2022). Total San Diego County population = 3,315,404. Note: These estimates do not reflect the 2020 decennial census counts.
  • ZIP codes with population <10,000 people were combined if they were not censored due to being Universities or Military areas.
  • Voter registration data for ZIP codes with Universities or Military areas are not shown because most people may be registered elsewhere, and the number of registered voters could be underestimated. The total number of registered voters for these ZIP codes is 2,725, the total population 64,130, and the percentage registered to vote is 4.2%.
  • The percentage of population registered to vote may approach, or exceed, 100%. The most recent population estimates may not reflect recent social and environmental changes of a community, possibly leading to an under- or overestimate of a population. Additionally, the number of registered voters by ZIP code is geocoded to a specific location while the population estimates are at the census tract level and appropriated to the ZIP code level. The appropriation of population estimates from one census tract to more than one ZIP codes may result in imprecise population estimates.  
  1. Ansolabehere, S., & Konisky, D. M. (2006). The introduction of voter registration and its effect on turnout. Political Analysis, 14(1), 83–100.
  2. U.S. Census Bureau. (n.d.). Current Population Survey (CPS). Retrieved April 4, 2023, from
  3. Fabina J. & Scherer, Z. (2022). Voting and Registration in the Election of 2020. Current Population Reports. Retrieved,
  4. These national statistics may not reflect the reasons people in San Diego County did not register to vote in the 2020 election, particularly due to varying voter laws and procedures across the United States. The Current Population Survey also only includes the non-institutionalized, civilian population of citizens 18 years of age or older residing in the United States; people living abroad that may cast absentee ballots are not included.
  5. According to State of California estimates that account for all voter eligibility criteria, 89.9% of eligible San Diego County residents were registered to vote as of August 30, 2021. The rate differs from what is presented here because the State has the resources to estimate the eligible population more accurately for the denominator; they consider other eligibility criteria in addition to age 18 years or older. California data by County: State report overall:
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Updated February 7, 2024