OBJECTIVES: To examine how youth and their caregivers’ mental health risk factors for suicide are associated with youth firearm access inside and outside the home. METHODS: This study examines a cross-section of the Adolescent Brain and Cognitive Development Social Development study data collected from 2016 to 2021. The sample included 2277 children aged 10 to 15 years from 5 study sites across the United States. We estimated multilevel generalized linear models of household firearm ownership and the child’s reported firearm access (hard access or easy access). The primary exposures were the child’s and their caregivers’ mental health risk factors for suicide. RESULTS: In the Adolescent Brain and Cognitive Development Social Development study sample, approximately 20% of children lived in a firearm-owning household and 5% of all children reported easy firearm access. In non–firearm-owning households, children with diagnosed lifetime suicidality were 2.48 times more likely (95% confidence interval [CI], 1.50–4.10) than their counterparts to report easy firearm access. In firearm-owning households, children of caregivers who self-reported any mental health history or externalizing problems were 1.67 times (95% CI, 1.10–2.54) and 2.28 times (95% CI, 1.55–3.37) more likely than their counterparts to report easy firearm access. CONCLUSIONS: Youths with mental health risk factors for suicide may be just as likely or more likely to report firearm access as those without such risk factors. Youth suicide prevention efforts should address youths’ firearm access outside the home and caregiver mental health.