ImportanceYoung adults in their 20s are at high relative risk for self- and other-directed firearm injury, but little is known about gun access patterns for this group.ObjectiveTo describe the longitudinal patterns of firearm access from childhood to young adulthood and to estimate whether violence experienced as a child or as an adult is associated with gun ownership in young adulthood.Design, Setting, and ParticipantsThe Great Smoky Mountains Study included participants from 11 contiguous, mostly rural counties in the Southeastern US. The first wave was completed in 1993 and the most recent in 2019. Periodic survey data were gathered in adolescence through participants’ late 20s. In 2023, adjusted Poisson regression with incident rate ratios (IRRs) and 95% CIs were used to estimate associations between violence and gun ownership in young adulthood in 3 age cohorts from the original sample.ExposuresViolent experiences in childhood (bullying, sexual and physical abuse, violent events, witnessing trauma, physical violence between parents, and school/neighborhood dangerousness) or adulthood (physical and sexual assault).Main Outcomes and MeasuresInitiating gun ownership was defined as no gun access or ownership in childhood followed by gun ownership at age 25 or 30 years. Maintaining gun ownership was defined as reporting gun access or ownership in at least 1 survey in childhood and ownership at age 25 or 30 years.ResultsAmong 1260 participants (679 [54%] male; ages 9, 11, and 13 years), gun access or ownership was more common in childhood (women: 366 [63%]; men: 517 [76%]) than in adulthood (women: 207 [36%]; men: 370 [54%]). The most common longitudinal pattern was consistent access or ownership from childhood to adulthood (373 [35%]) followed by having access or ownership in childhood only (408 [32%]). Most of the violent exposures evaluated were not significantly associated with the outcomes. Being bullied at school was common and was associated with reduced ownership initiation (IRR, 0.76; 95% CI, 0.61-0.94). Witnessing a violent event was significantly associated with increased probability of becoming a gun owner in adulthood (IRR, 1.24; 95% CI, 1.03-1.49).Conclusions and RelevanceIn this cohort study, gun ownership and access were transitory, even in a geographic area where gun culture is strong. Early adulthood—when the prevalence of gun ownership was relatively low—may represent an opportune time for clinicians and communities to provide education on the risks associated with firearm access, as well as strategies for risk mitigation.