Temporary college closures in response to the COVID-19 pandemic created an exodus of students from college towns just as the decennial census count was getting underway. We use aggregate cellular mobility data to evaluate if this population movement affected the distributional accuracy of the 2020 Census. Based on the outflow of devices in late March 2020, we estimate that counties with a college were undercounted by two percent, likely affecting Congressional apportionment. For college towns, student populations can impact government funding allocations, policy program decisions, and planning for infrastructure, public health, and more. The Census Bureau is allowing governmental entities to request count reviews through June 2023. Colleges should cooperate with state and local government efforts to ensure an accurate count.