Objective To describe the prevalence of and factors associated with firearm ownership; the types, subtypes and quantity of firearms owned; and when, where and why firearms were acquired in California.

Methods A cross-sectional analysis of a state-representative, probability-based, internet survey of California adults was conducted in September–October 2018 (n=2558; completion rate 49%). Household firearm ownership was ascertained for all respondents; personal firearm ownership was ascertained only among respondents who reported living in a home with firearms; and information on the types and quantity of firearms owned and details about recently acquired firearms came from firearm owners only.

Findings Roughly one in four (25%, 95% CI 22% to 28%) California adults live in a home with a firearm, including 4.2 million adults—14% (95% CI 13% to 16%) of the adult population—who personally own a firearm. These owners collectively own an estimated 19.9 million firearms (8.9 million handguns). Approximately half (48%, 95% CI 34% to 61%) of the firearm stock in California is owned by the 10% (95% CI 6% to 14%) of owners who own 10 or more firearms, though more than half (54%, 95% CI 47% to 62%) of owners in the state own only one or two firearms. Most (69%, 95% CI 63% to 75%) owners purchased their last firearm from a firearm retailer, usually a handgun purchased primarily for protection against people.

Conclusion This study provides the most detailed and up-to-date information available on firearm ownership and acquisition in California. Results can inform firearm violence prevention efforts and public health, safety and policy development in California and nationally.