Green infrastructure solutions, such as rain gardens, are widely recognized for their ability to improve water quality and mitigate water quantity issues while offering numerous co-benefits. However, the performance of green infrastructure, which relies on dynamic living components (e.g., plants, soil biota), evolves over time and is influenced by various external inputs and conditions. These changes can range from site-scale human decisions (maintenance and management), to landscape-scale hydrologic changes (urbanization), to global-scale effects of climate change (altered precipitation patterns). We examine the state of research concerning long-term ecological and hydrological (eco-hydrologic) performance of rain gardens, focusing on those studied 9 years post-installation or greater. We explore the history of rain garden implementation, highlight case studies demonstrating long-term research, and identify gaps in our understanding of how rain gardens function over time. Our findings emphasize the lack of long-term data and the need to investigate the responses of aging green infrastructure to ensure its successful integration into a changing world. A comprehensive understanding of how green infrastructure effectiveness changes over time will inform better policies, maintenance practices, design improvements, and planning strategies aimed at increasing resilience.