How did mail-in voting affect voter turnout in California's 2024 presidential election?

1. Bold claims pulled from the record — what people are asserting and why it matters

Analysts make three core claims about mail-in voting and turnout in California’s 2024 presidential contest: first, that turnout declined substantially from 2020 despite more registered and eligible voters (roughly 16 million ballots in 2024 versus ~17.7 million in 2020), a drop framed as the largest 50-year decline when measured against eligible residents ^[2]. Second, official certification shows a large share of ballots were mail-in — Secretary of State data reports over 13 million Vote By Mail ballots in 2024, about 81% of ballots cast, even as turnout percentage sat near 71.43% of registered voters in some accounts and 59.97% by other tabulations depending on denominator choices ^{[1] [4]}. Third, researchers and policy briefs argue the Voter’s Choice Act and universal mailing of ballots have mixed localized effects, sometimes raising participation for specific groups or counties and sometimes not ^{[5] [6]}. These competing claims matter because they reshape policy debates over whether expanding mail access should be a priority to raise turnout or whether other interventions are needed.

2. What official returns and statistics actually show — the raw numbers and how they fit together

California’s certified returns show heavy reliance on mail ballots and a turnout level comparable to pre-2020 presidential years, but lower than the exceptionally high 2020 benchmark. The Secretary of State certification indicates 71.43% of registered voters cast ballots in 2024 with 13,034,378 Vote By Mail ballots, which was a large share of total votes; the state’s Statement of Vote lists 26.9 million registered voters and about 16.14 million votes cast, giving a 59.97% turnout when using the broader denominator in county-level participation statistics ^{[1] [4]}. Different ways of measuring turnout — percentage of registered voters versus percentage of eligible residents — produce divergent impressions. Analysts note that 2020 was an outlier year with extraordinarily high participation, making comparisons fraught without accounting for registration drives and pandemic-era voting dynamics ^[2]. The raw data thus show high mail use but ambiguous net effects on turnout.

3. County-level variation and conflicting study findings — the story is not uniform across California

County-level breakdowns reveal heterogeneous effects: some counties with very high Vote By Mail usage also showed high turnout (Alpine, Plumas), while populous counties like Los Angeles had lower turnout despite substantial mail voting shares ^{[7] [4]}. Policy research on the Voter’s Choice Act finds inconsistent patterns: counties that adopted the Act experienced mixed turnout changes over different election cycles, with some improvement among young and Latino voters in 2024 but a pronounced drop among Black voters in some analyses ^[5]. Likewise, mail-in ballot acceptance rates in primaries were very high — over 98% acceptance — indicating administrative effectiveness in processing mail ballots, but that metric speaks to ballot integrity not to motivational impacts on turnout ^[8]. This patchwork means local context, outreach, and demographic composition strongly mediate whether mailed ballots translate into higher participation.

4. Explanations, confounders, and policy context that researchers emphasize

Analysts identify several factors that confound simple causal claims linking mail ballots to turnout. Automatic Voter Registration and enrollment expansions likely added many less-engaged registrants, depressing turnout measured as a share of registrants even if absolute votes stayed high ^[2]. Shifts in voter preference toward early in-person voting nationwide also changed the mix of methods: federal reporting shows mail-in rates fell nationally in 2024 while early in-person surged, suggesting method substitution rather than a net mobilization effect ^[3]. The extraordinary baseline in 2020 (pandemic-driven changes, unprecedented mobilization) means 2024 may reflect a normalization rather than a failure of mail voting. Analysts therefore caution that causation is hard to establish without modeling controls for registration composition, targeted outreach, and county election administration differences ^{[3] [6]}.

5. Bottom line: what we can reliably say and what remains unsettled

The reliable, evidence-based bottom line is that mail-in voting was widely used and effectively administered in California’s 2024 presidential election, but it did not produce a statewide turnout surge compared with 2020; turnout declined by about 1.7 million ballots in absolute terms and by notable percentage points depending on the denominator used ^{[2] [1]}. Whether mail ballots caused the decline is unresolved: local analyses show both gains and losses tied to mail strategies and the Voter’s Choice Act, and broader shifts in registration and voting preferences create alternative explanations ^{[5] [6]}. Policymakers should therefore treat mail access as one component of a broader turnout strategy while commissioning targeted, causal studies that control for registration changes and county heterogeneity before using 2024 alone to draw definitive lessons ^{[8] [2]}.