Context: Reductions in population mobility can mitigate virus transmission and, in turn, disease-related mortality. But do social distancing policies in response to COVID-19 actually change population behavior and, if so, what political, socioeconomic, and epidemiological factors condition this policy effect?Methods: We leverage subnational variation in the stringency and timing of state-issued social distancing policies to test their effects on population mobility from March to December 2020 across 109 states in Brazil, Mexico, and the United States. We also explore how conventional explanations of compliance, including political trust, socioeconomic resources, health risks, and partisanship, modify these policy effects.Findings: In Brazil and the U.S., mandatory stay-at-home orders and workplace closures jointly reduced mobility, especially early in the pandemic. In Mexico, where federal government intervention created greater policy uniformity across states, workplace closures produced the most consistent reduction in mobility. Conventional explanations of compliance perform well in the U.S. but not in Brazil and Mexico, with the exception of socioeconomic resources.Conclusions: In addition to new directions for future research on the politics of compliance, the article offers insights for policymakers about which public health measures are likely to elicit compliance. Our finding that the efficacy of workplace closures at reducing population mobility increases with levels of socioeconomic development suggests that cash transfers, economic stimulus packages, and other policies that mitigate the financial burdens of the pandemic may help reduce population mobility by decreasing the costs of staying at home.