Youth depression is a significant and growing international public health problem. Youth who engage in high levels of delinquency are at particularly high risk for developing problems with depression. The present study examined the impact of a behavioral intervention designed to reduce delinquency (Treatment Foster Care of Oregon; TFCO) compared to a group care intervention (GC; i.e., services as usual) on trajectories of depressive symptoms among adolescent girls in the juvenile justice system. TFCO has documented effects on preventing girls’ recidivism, but its effects on preventing the normative rise in girls’ depressive symptoms across adolescence have not been examined. This indicated prevention sample included 166 girls (13–17 years at T1) who had at least one criminal referral in the past 12 months and who were mandated to out-of-home care; girls were randomized to TFCO or GC. Intent-to-treat analyses examined the main effects of TFCO on depression symptoms and clinical cut-offs, and whether benefits were greatest for girls most at risk. Depressive symptom trajectories were specified in hierarchical linear growth models over a two year period using five waves of data at six month intervals. Depression clinical cut-off scores were specified as nonlinear probability growth models. Results showed significantly greater rates of deceleration for girls in TFCO versus GC for depressive symptoms and for clinical cut-off scores. The TFCO intervention also showed greater benefits for girls with higher levels of initial depressive symptoms. Possible mechanisms of effect are discussed, given TFCO’s effectiveness on targeted and nontargeted outcomes.