Background: The COVID-19 pandemic has presented unique challenges across the world in getting citizens to change their behaviors in response to a public health crisis. In the United States, it appears that partisan differences in willingness to comply with these measures have emerged: Democrats are typically more supportive than Republicans in their stated support of and willingness to comply with these measures. However, actual behaviors are notoriously hard to accurately capture with survey items. Objective: To determine the extent to which county-level partisanship influences average willingness to stay at home, and how these effects are moderated by county level characteristics. Methods: We use personal device (cell phone) data provided by SafeGraph, aggregated at the county-level, to determine how county-level partisanship is correlated with willigness to stay at home. We additionally test whether these effects are conditional upon the prevalence of COVID-19 in the county, and the percentage of the county under 30 years old. Results: We find that county-level partisanship predicts aggregate level compliance with social distancing behavior—citizens of counties that are more Republican spend more time away from home than Democratic counties. We find that the number of COVID-19 cases in the county and the percentage of the county under the age of 30 moderate these effects. Conclusion: Partisanship appears to be a powerful predictor, at the county-level, of willigness to follow stay at home orders in the early stages of the COVID-19 pandemic.