Since the spring of 2021, nearly 700 colleges and universities in the U.S. have mandated that their students become vaccinated against the COVID-19 virus. We leverage rich data on colleges' vaccination policies and semester start dates, along with a variety of county-level public health outcomes, to provide the first estimates of the effects of these mandates on the communities surrounding four-year, residential colleges. In event study specifications, we find that, over the first 13 weeks of the fall 2021 semester, college vaccine mandates reduced new COVID-19 cases by 339 per 100,000 county residents and new deaths by 5.4 per 100,000 residents, with an estimated value of lives saved between $9.7 million and $27.4 million per 100,000 residents. These figures suggest that the mandates reduced total US COVID-19 deaths in autumn 2021 by approximately 5%.