Adverse childhood experiences (ACEs) are social determinants of health that increase morbidity and mortality and are prevalent among juvenile justice–involved (JJI) youth. ACEs drive health‐risk behaviors (e.g., substance use) that reflect maladaptive coping, increase arrest risk, and overlap with posttraumatic risk‐seeking theoretically and reckless/self‐destructive behaviors diagnostically. However, little is known, especially among girls, about cumulative developmental adversity burden distress (i.e., total cumulative/lifespan stressor reactivity, grief‐specific and adversity‐related symptoms, and adversity‐driven maladaptive coping strategies by age 18) and associated health risk impacts. Therefore, we assessed (a) developmental adversity burden indicators capturing expanded ACEs (E‐ACEs; reflecting cumulative losses and traumatic events), cumulative distress, and risk characteristics; (b) potential racial/ethnic differences in developmental adversity burden; and (c) predictors of maladaptive coping among 223 JJI girls. Participants averaged 15 E‐ACEs, endorsing 61.0% of stressor reactivity reactions, 58.4% of cumulative grief‐specific symptoms, 55.7% (avoidance) to 73.2% (arousal) of adversity‐related symptoms, and 45.0% of adversity‐driven maladaptive coping strategies. White JJI girls endorsed significantly higher stressor reactivity and maladaptive coping than Latina girls (e.g., 38.8% vs. 14.6% suicide attempts), ds = 0.56–0.71. Adaptive LASSO analyses of maladaptive coping highlighted primary contributions from stressor reactivity, arousal alterations (excluding reckless/self‐destructive behaviors), and cognition/mood alterations but not E‐ACEs, grief, avoidance, or intrusions. Participants reported high levels of all cumulative developmental adversity burden indicators (e.g., 81.6% reported reckless/self‐destructive behaviors). Results support cumulative, adversity‐informed, universal precautions and assessments. Further, emotion regulation interventions targeting stressor reactivity, cognition/mood alterations, and/or arousal alterations may be useful for JJI youth with maladaptive coping.