Objective: To compare the mental health of undergraduates before the COVID-19 pandemic lockdown to their mental health one year later. Participants: Data from the American College Health Association (ACHA)'s National College Health Assessment III (ACHA-NCHAIII) were used, averaging a sample size of 54,844 undergraduate students and 106 schools nationwide per time point of assessment in the study. Methods: Secondary analyses of the ACHA-NCHAIII compared undergraduates' scores on five measures of mental health measures (loneliness, psychological distress, suicidality, flourishing, and resilience) from Spring 2020 to Spring 2021. Results: Undergraduates' responses showed an increase in loneliness, psychological distress, and suicidality as well as a decrease in flourishing and resilience. Conclusions: The worsening of undergraduates' mental health calls for greater action by schools to alleviate students' distress and improve their wellbeing.