Objectives The COVID pandemic has had widespread impacts on maternal mental health. This research aims to examine the relationship between psychosocial stressors and symptoms of depression and anxiety and the extent to which emotional support or resilient coping moderates the relationship between psychosocial stressors and maternal mental health during the first wave of the COVID pandemic. Methods This analysis includes data collected in October and November 2020 from a geographically and sociodemographically diverse sample of 776 mothers in the U.S. with children <= 18 years of age. Log binomial models were used to estimate the association between moderate or severe symptoms of anxiety and depression and psychosocial stressors. Results Symptoms of moderate or severe anxiety and depression were reported by 37.5% and 37.6% of participants, respectively. Moderate (aRR 2.76 [95% CI 1.87, 4.07]) and high (aRR 4.95 [95% CI 3.40, 7.20]) levels of perceived stress were associated with greater risk of moderate or severe anxiety symptoms. Moderate and high levels of parental burnout were also associated with greater prevalence of moderate or severe anxiety symptoms in multivariable models. Results were similar when examining the relationship among stress, parental burnout, and depressive symptoms. Neither resilient coping nor social support modified the relationship between psychosocial stressors and mental health. Conclusions for Practice Evidence-based strategies to reduce stress and parental burnout and improve the mental health of mothers are urgently needed. Strategies focused on bolstering coping and social support may be insufficient to improve maternal mental health during acute public health emergencies.