Objective: This study explored how COVID-related mental health and well-being varied between undergraduate and graduate students. Relationships with physical health behaviors were also examined. Participants: Undergraduate (n = 897) and graduate (n = 314) students were recruited from three US universities between mid-April and late-May 2020. Methods: Participants in this cross-sectional survey self-reported perceived stress, financial stress, resilience, repetitive negative thinking, mood, anxiety, diet, sleep, and physical activity using validated instruments. Results: Undergraduate students reported more perceived stress, more repetitive negative thinking, less positive mood, and less support from professors than graduate students. Perceived stress, repetitive negative thinking, negative mood, and anxiety increased among all students (p < 0.05 for all). Correlations between mental health outcomes and physical health behaviors were weak to moderate (r = 0.08 to 0.49). Conclusions: College students, particularly undergraduates, perceived negative mental health impacts during COVID. Creative approaches for meeting student needs are necessary.