Objectives: This study examines national trends in the prevalence, risk factors, and treatment of depression among adolescents and investigate disparities in their mental health service use in the US. Methods: Data for adolescents aged 12 to 17 years (N = 95,856) who participated in the annual, cross-sectional National Survey on Drug Use and Health (NSDUH) from 2011 to 2016 were pooled and analyzed. Time trends and predictors of adolescents' depression and treatment were examined using Pearson's χ² test and multivariable logistic regression. Results: The prevalence of adolescents' 12-month depression increased steadily from 8.3% to 12.9% over the years, but their use of mental health services remained largely stable. Higher rates of depression were observed in females, older adolescents, and those from single-mother households. Having less authoritative parents and negative school experiences significantly predicted adolescent depression. Lower rates of treatment and medication use were found among racial/ethnic minorities and adolescents without any insurance. Whereas having less authoritative parents decreased adolescents' likelihood of using healthcare services, negative school experiences significantly increased their chances of using treatments and medication. Conclusions: A growing number of adolescents with untreated depression were noted over time. Enhanced psychoeducation, continued policy efforts, and expanded service capacity are warranted.