Opioid misuse (OM) is a priority public health concern, especially for those in correctional settings. Understanding the etiology of OM among justice-involved children (JIC) is key to resolving this crisis. On average, 12% of all children and up to 50% of JIC in the United States have experienced household substance misuse (HSM). Theory and empirical research suggest that HSM may increase risk for OM, but these relationships have not been examined among JIC. The objective of this study was to examine the effects of sibling and parent substance misuse on OM among JIC. Cross-sectional data on 79,960 JIC from the Florida Department of Juvenile Justice (FLDJJ) were examined. Past 30-day opioid (P30D) OM was indicated by urine analysis. Bivariate and multivariate logistic regression analyses were employed. In the total sample, nearly 3% met FLDJJ criteria for P30D OM and nearly 25% lived with a parent/caregiver or sibling who misused substances. Among opioid misusers, one third lived with a parent/caregiver who misused substances and nearly half lived with a parent/caregiver or sibling who misused substances. Compared to JIC without HSM, JIC reporting sibling substance misuse had 1.95 times higher odds of OM (95% CI, 1.63–2.33), JIC with parent substance misuse had over twice the odds of OM (95% CI, 1.89–2.31), and those with both sibling and parent had more than three times higher odds of OM (95% CI, 2.75–3.87). Family-based approaches to OM intervention and prevention initiatives may be more effective than individual-focused approaches. Implications are discussed.