To analyze the effectiveness of social distancing in the United States (U.S.).
A novel cell-phone ping data was used to quantify the measures of social distancing by all U.S. counties.
Using a difference-in-difference approach results show that social distancing has been effective in slowing the spread of COVID-19.
As policymakers face the very difficult question of the necessity and effectiveness of social distancing across the U.S., counties where the policies have been imposed have effectively increased social distancing and have seen slowing the spread of COVID-19. These results might help policymakers to make the public understand the risks and benefits of the lockdown.