Our main finding is that mask mandates and use are not associated with lower SARS-CoV-2 spread among US states. 80% of US states mandated masks during the COVID-19 pandemic. Mandates induced greater mask compliance but did not predict lower growth rates when community spread was low (minima) or high (maxima). We infer that mandates likely did not affect COVID-19 case growth, as growth rates were similar on all days between actual or modeled issuance dates and 6 March 2021. Higher mask use (rather than mandates per se) has been argued to decrease COVID-19 growth rates…. Higher mask use did not predict lower maximum growth rates, smaller surges, or less Fall-Winter growth among continental states. Mask-growth rate correlation was only evident at minima. This may be an artifact of faster growth at fewer normalized cases, as well as regional differences in case prevalence early in the pandemic. States in the high mask quintile grew at similar rates as states in the low mask quintile after maxima (when interstate total case differences were smaller than before minima).