Public stigma is a pervasive barrier that prevents many individuals in the U.S. from engaging in mental health care. This systematic literature review aims to: (1) evaluate methods used to study the public's stigma toward mental disorders, (2) summarize stigma findings focused on the public's stigmatizing beliefs and actions and attitudes toward mental health treatment for children and adults with mental illness, and (3) draw recommendations for reducing stigma towards individuals with mental disorders and advance research in this area. Public stigma of mental illness in the U.S. was widespread. Findings can inform interventions to reduce the public's stigma of mental illness.