The broad impact of the COVID-19 on self-reported daily behaviors and health in Chinese and US samples remains unknown. This study aimed to compare physical and mental health between people from the United States (U.S.) and China, and to correlate mental health parameters with variables relating to physical symptoms, knowledge about COVID-19, and precautionary health behaviors. To minimize risk of exposure, respondents were electronically invited by existing study respondents or by data sourcing software and surveys were completed via online survey platforms. Information was collected on demographics, physical symptoms, contact history, knowledge about COVID-19, psychologic parameters (i.e. IES-R; DASS-21), and health behaviors. The study included a total of 1445 respondents (584 U.S.; 861 China). Overall, Americans reported more physical symptoms, contact history, and perceived likelihood of contracting COVID-19. Americans reported more stress and depressive symptoms, while Chinese reported higher acute-traumatic stress symptoms. Differences were identified regarding face mask use and desires for COVID-19 related health information, with differential mental health implications. Physical symptoms that were possibly COVID-19 related were associated with adverse mental health. Overall, American and Chinese participants reported different mental and physical health parameters, health behaviors, precautionary measures, and knowledge of COVID-19; different risk and protective factors were also identified.