Background The mental health of racial/ethnic minority groups in the United States may be disproportionately impacted by the COVID-19 pandemic due to greater experience of peri-pandemic stressors. Yet, few studies have systematically examined racial/ethnic differences in mental health outcomes in this context. Methods Data came from the COVID-19 Southern Cities Study, a probability-based, cross-sectional study conducted in May/June 2020 among adults living in the metropolitan statistical areas of Atlanta, Austin, Dallas, Houston, and New Orleans. Unadjusted and adjusted associations between racial/ethnic identity and past-week depression and/or anxiety symptoms (Patient Health Questionnaire-2 score ≥ 3 or Generalized Anxiety Disorder-2 score ≥ 3), trouble sleeping, physical reactions when thinking about COVID-19, and self-rated worsened mental health due to the pandemic were estimated in separate logistic regression models. Results Over 30% of respondents reported depression and/or anxiety symptoms, 21% reported physical reactions, 25% had trouble sleeping, and 33% worsened mental health since the pandemic began. Adjusting for sociodemographic and health-related characteristics and pandemic-related stressors, odds of anxiety symptoms (odds ratio (OR) 0.53, 95% confidence interval (CI) 0.30–0.95) and worsened mental health (OR 0.58, 95% CI 0.36–0.94) were lower among non-Hispanic Black vs. non-Hispanic white respondents. Limitations No diagnostic assessments were used, and results may not be generalizable to later phases of the pandemic and the entire U.S. South. Conclusions Despite greater pandemic-related stressor experience, poor mental health outcomes were not more common among racial/ethnic minority individuals. However, interventions to reduce disparities in stressor experience and promote mental health are needed.