Sehra ST, George M, Wiebe DJ, et al. - This study was attempted to ascertain whether cell phone location data are correlated with the rate of change in new COVID-19 cases by county across the US. Between January 22, 2020, and May 11, 2020, this cohort study incorporated publicly available county-level daily COVID-19 case data, and county-level daily cell phone location data made publicly available by Google. Between 949 and 2,740 US counties and between 22,124 and 83,745 daily observations were studied depending on the availability of cell phone data for that county and day. The data support the hypothesis that greater reductions in cell phone activity in the workplace and retail locations, and greater increases in activity at the residence, are correlated with lesser growth in COVID-19 cases. These findings give support for the value of monitoring cell phone location data to anticipate future trends of the pandemic.