To better understand social sustainability in the context of rapid boom growth and decline, we examine longitudinal social change in the modern boomtown of Colstrip, MT. Using a mixed-methods approach that includes two waves of a community survey—administered in 1996 and 2018, respectively—and focus groups conducted in 2018–2019, we explore shifts in residents’ sense of community as well as their perceptions and attitudes about current challenges to their community’s future and sustainability. We show that, despite surviving previous boom and bust periods related to changes in the coal industry, this community now faces a new reality that involves the closure of all local power plants. However, both survey responses and residents’ narratives indicate a strong sense of community and support for developing strategies that address challenges to the town’s future. This exploratory case study helps to extend the literature by contributing to a greater understanding of the experiences of contemporary workers who individually migrated to a small, rural energy town but who now, as a community, face an uncertain future, and by illuminating the role of sense of community in both social and environmental sustainability efforts.