Insecurity in housing, nutrition, utilities, and income are recognized correlates of community firearm violence, yet little research has assessed whether public policies that support access to these basic needs help prevent community firearm violence. During the COVID-19 pandemic, several counties enacted policies to mitigate the economic consequences of the pandemic by offering different types of economic supports. We estimated the impact of these policies on firearm assault injuries across 31 California counties from January 2020 to December 2022. We analyzed weekly county-level population-representative data on policies from the US COVID-19 County Policy Database, firearm assault injuries from statewide emergency department and inpatient hospitalization discharge records, and confounding variables from multiple public sources. Using modern causal inference method and adjusting for potential confounders, we compared changes in firearm assault injury rates associated with each type of policy enacted as-observed versus the rates had all counties prematurely stopped the given policy on a specified date. Across the 4,836 county-weeks of observation, the average weekly firearm assault injury rate was 0.18 per 100,000 people. Nutrition support policies were associated with lower rates of firearm assault injuries (Risk Difference [RD] per 100,000  -0.143; 95% CI, -0.099, -0.187), as were paid sick leave policies (RD, -0.079; 95% CI, -0.099, -0.059), but only for certain pandemic periods (through April 2021 and after October 2021, respectively). Housing protections, unemployment supports, other income supports, or utilities payment supports were not associated with firearm assault injuries. Associations varied by racial/ethnic group, gender, and age group. This study adds to a small but growing literature on the potential effectiveness of economic support policies in reducing community firearm violence.