Recent years have seen an increase in the use of social media for various decision-making purposes in the context of urban computing and smart cities, including management of public parks. However, as use of readily available social media becomes more mainstream, a critical concern that arises is the extent to which such data remains a valid proxy for people’s online and offline behavior over time. Existing literature has mostly concentrated on the endogenous elements of the biases of social media data corresponding to platform popularity across different demographics, but failed to address the exogenous factors. In this article, we conduct a longitudinal study of park visitors and the impact of pandemic on park visitation in four US metropolitan areas. By leveraging data from Instagram and SafeGraph, we show the consequences of not accounting for both endogenous and exogenous biases that exists in approaches that rely on social media to estimate park visitation.