IntroductionMajor depression is a common and potentially lethal condition. Early data suggest that the population-level burden of depression has been exacerbated by the COVID-19 pandemic. Prepandemic estimates of depression prevalence are required to quantify and comprehensively address the pandemic's impact on mental health in the U.S.MethodsData were drawn from the 2015–2020 National Survey on Drug Use and Health, a nationally representative study of U.S. individuals aged ≥12 years. The prevalence of past-year depression and help seeking for depression were estimated from 2015 to 2019, and time trends were tested with Poisson regression with robust SEs. Point estimates were calculated for 2020 and not included in statistical trend analyses because of differences in data collection procedures.ResultsIn 2020, 9.2% (SE=0.31) of Americans aged ≥12 years experienced a past-year major depressive episode. Depression was more common among young adults aged 18–25 years (17.2%, SE=0.78), followed closely by adolescents aged 12–17 years (16.9%, SE=0.84). Depression increased most rapidly among adolescents and young adults and increased among nearly all sex, racial/ethnic, income, and education groups. Depression prevalence did not change among adults aged ≥35 years, and the prevalence of help seeking remained consistently low across the study period.ConclusionsFrom 2015 to 2019, there were widespread increases in depression without commensurate increases in treatment, and in 2020, past 12‒month depression was prevalent among nearly 1 in 10 Americans and almost 1 in 5 adolescents and young adults. Decisive action involving a multipronged public health campaign that includes evidence-based prevention and intervention to address this ongoing mental health crisis is urgently needed.