"In the current pandemic, epidemiologists and public health officials have strongly encouraged people to physically distance from one another. Numerous studies have shown that physical distancing effectively stopped the exponential spread of COVID-19 at its onset, preventing the inundation of healthcare providers and saving numerous lives. To determine whether physical distancing differs as a function of partisanship, we examined whether the political leaning of over 3,000 counties in the United States is linked to the extent to which residents of those counties practised physical distancing behaviours during the first few months of the pandemic (March–May 2020). Specifically, we analysed the aggregated Global Positioning System (GPS) coordinates of approximately 15 million people across the United States per day (tracked via smartphone location coordinates) to quantify the degree of physical distancing in each US county. Physical distancing was measured in terms of reduction in general movement and reduction in visiting non-essential services (for example, restaurants). Furthermore, to examine the association between party identity and public health, we tested whether partisan differences in physical distancing mediate the relationship between partisanship and COVID-19 infection and fatality growth rates. Critically, in testing these questions we anticipated that what could appear to be partisan differences in physical distancing may actually reflect social or economic third variables. For instance, liberal areas in the United States experienced higher levels of COVID-19 infections and fatalities at the start of the pandemic (early March 2020) and thus may have perceived COVID-19 as more dangerous and engaged in greater preventative measures. To account for this and other possible explanations, we included numerous covariates in our models when testing partisan differences in physical distancing and health outcomes."