The degree to which many benefits of national parks are realized hinges on public access. Traditional methods in estimating park visitation can be time-consuming, costly, and labor-intensive. Fortunately, the growing availability of ‘big data’ offers new opportunities for rapid and large-scale estimation. This study investigated the spatiotemporal dynamics in visitation to all National Park Service (NPS) units in the contiguous U.S. and explored associated sociodemographic factors using fine-grained SafeGraph mobile device location data. We found that people tend to travel less frequently and in a shorter distance to visit NPS units in both 2020 and 2021 vs. 2019. During the pandemic, people preferred visiting national parks and nature-based NPS units over culture-oriented ones relative to pre-pandemic levels. Most importantly, this study highlights a long-standing social inequity – the groups of minorities (i.e., Blacks, Asians, and Hispanics) and lower-income were less likely to visit NPS units than Whites and higher-income, respectively.