In this study, we report the prevalence of self-reported secondhand smoke (SHS) exposure in homes and vehicles among US middle and high school students in 2019 and changes in SHS exposure over time. Data were from 7 years of the National Youth Tobacco Survey (NYTS; 2011, 2013, and 2015-2019). In 2019, 25.3% (an estimated 6.7 million) of students reported home SHS exposure and 23.3% (6.1 million) reported vehicle SHS exposure. Home and vehicle SHS exposure significantly declined during 2011 through 2018, except for home exposure among non-Hispanic black students. Implementation of smoke-free policies in public and private settings can reduce SHS exposure.