Cross-sectoral collaborations (XSPs) are promising solutions to addressing societal problems. Yet the understanding is limited regarding how these collaborations unfold when they are bounded in a geographical location (i.e., place-based) and organizations need to repeatedly collaborate due to limited choice of partners. To develop insights into the dynamics in place-based XSPs, we conducted a qualitative study of the collaborations between a National Health Service hospital and third-sector organizations in a community located in the East England area. We found that informal relationships play crucial roles and interact with formal relationships to drive place-based XSPs. We demonstrated how the shadow of the past and the shadow of the future jointly affect XSPs in both positive and negative ways, shaping the management of challenges in these collaborations. Moreover, we revealed the unique externalities of placed-based XSPs. Integrating our findings, we developed a model to theorize how different components interact in place-based XSPs and the associated outcomes. By bringing the role of places to the surface, we provide a comprehensive depiction of the dynamics in place-based collaborations and contribute to the literature on XSPs and on interorganizational relationships.