This entry investigates the impact of the COVID-19 pandemic public health interventions on the mental health of individuals with pre-existing mental illnesses. It highlights the unique challenges faced by this population, including disruptions in mental healthcare access, increased social isolation, and economic hardships. This entry further examines mitigation strategies employed to support their well-being, such as telehealth, virtual mental health services, online support groups, and volunteer-led local community psychiatry services. Finally, it proposes public health planning strategies to better support mental health during future crises.