People experiencing homelessness have a disproportionate burden of mental illness and mortality than those who are not homeless. The environment in congregate shelter accommodation may significantly contribute to this health burden, particularly regarding mental health. Housing insecurity significantly increases risk of presenting to the emergency department in behavioral crises. In recent years, many cities implemented programs diverting congregate shelter residents, most commonly to hotel accommodation. There is some evidence that the shift to non-congregate living may have had a positive impact on people’s mental health. Connecticut localities are planning new policies designed to build on lessons learned from that period, providing non-congregate options through healthcare-community partnership organizations to people who are unhoused. Understanding the mental health effects of non-congregate shelter options is essential to inform these developing policy reforms and innovations. This project will use a Community Based Participatory Research transformative approach, with a multistage convergent parallel mixed methods design, to measure the impact of healthcare-housing community partnerships that support non-congregate living interventions on mental health. We will conduct the study in Connecticut, where a state-wide implementation of non-congregate shelter policies from 2020-2022 presents a unique opportunity to examine the relationship between housing interventions and mental health outcomes. This context presents an unprecedented opportunity to study the relationship between shelter interventions and mental health outcomes. We will aim to study the impact of both the above-mentioned shelter policies and developing and ongoing housing initiatives on mental health crises by: 1) Qualitatively exploring mechanisms between non-congregate housing policies and mental illness including a landscape analysis to characterize processes through which shelter and healthcare providers partner to address housing needs, building on strong existing relationships with stakeholders and people experiencing homelessness; 2) Characterizing the effect of Connecticut’s hotel-based temporary shelter program on mental health crises among patients experiencing homelessness who were diverted from congregate shelters to hotel rooms during between 2020 and 2022 compared to a control site in Alabama using data from electronic medical records to perform a difference-in- differences identification strategy; and 3) Prospectively evaluating, using mixed methods, the impact of current housing policies that offer non-congregate living options on mental health, including non-congregate spaces in existing shelters, and newer potential policies such as tiny house villages. Findings from this study have the potential to inform policies and procedures of healthcare-housing community partnerships and improve mental health among those experiencing homelessness.