Background: Containment of the COVID-19 pandemic requires evidence-based strategies to reduce transmission. 11 Because COVID-19 can spread via respired droplets, many states have mandated mask use in public settings. 12 Randomized control trials have not clearly demonstrated mask efficacy against respiratory viruses, and 13 observational studies conflict on whether mask use predicts lower infection rates. We hypothesized that statewide 14 mask mandates and mask use are associated with lower COVID-19 case growth rates in the United States. 15 Methods: We calculated total COVID-19 case growth and mask use for the continental United States with data from 16 the Centers for Disease Control and Prevention and Institute for Health Metrics and Evaluation. We estimated post-17 mask mandate case growth in non-mandate states using median issuance dates of neighboring states with mandates. 18 Results: Case growth was not significantly different between mandate and non-mandate states at low or high 19 transmission rates, and surges were equivocal. Mask use predicted lower case growth at low, but not high 20 transmission rates. Growth rates were comparable between states in the first and last mask use quintiles adjusted for 21 normalized total cases early in the pandemic and unadjusted after peak Fall-Winter infections. Mask use did not 22 predict Summer 2020 case growth for non-Northeast states or Fall-Winter 2020 growth for all continental states. 23 Conclusions: Mask mandates and use are not associated with slower state-level COVID-19 spread during COVID-24 19 growth surges. Containment requires future research and implementation of existing efficacious strategies.