Given the global impact of coronavirus disease 2019 (COVID-19) on mental and physical health, we examined young adults' changes in mental health, intimate relationship quality, alcohol use and weight-related behaviors during COVID-19 and their correlates (depressive symptoms, resilience, social context and COVID-19-related factors). We analyzed data from a longitudinal study of 1082 young adults across six metropolitan areas (M[subscript age] = 24.76 ± 4.70; 51.8% female; 73.6% White and 12.5% Hispanic), using multivariate linear regressions for continuous outcomes (magnitude of mental health impact) and logistic regressions for categorical outcomes (decreased relationship quality, physical activity and nutrition and increased alcohol use and sedentary behavior). Of five negative mental health impacts assessed, participants reported experiencing an average of 3.54 (SD = 5.46), experiencing more correlated with increased childcare responsibilities and lower resilience. Additionally, 23.6% of those in relationships experienced negative relationship impact, 41.3% increased alcohol use, 47.2% decreased physical activity, 74.0% were more sedentary and 34.7% experienced poorer nutrition, all of which was predicted by greater depressive symptoms. Additionally, lower resilience predicted negative relationship impact and poorer nutrition and social context/roles correlated with various outcomes (e.g. relationships and alcohol use). Interventions to reduce negative health behaviors given societal stressors should address key psychosocial and situational factors, including depressive symptoms and resilience.