Project Summary/Abstract Mental health inequities among Black adults in the United States are stark. In 2020, the prevalence of past-year any mental illness based on a DSM diagnosis was 17% among Black adults (over 7 million people). In perspective, that number is more than the combined populations of Chicago IL, Houston TX, and Philadelphia PA. Black adults tend to be diagnosed with mental health conditions that are more severe, persist longer, and have debilitating social consequences. Socio-structural and environmental stressors such as racial discrimination, police brutality, and persistent poverty are well-documented predictors of poor mental health among Black people. Social connectedness is directly associated with improved mental health and buffers the negative impact of several health risk factors such as social isolation. Yet, research on social connectedness and mental health among Black adults remains limited. This paucity of work reflects a critical gap in knowledge regarding a psychosocial protective factor that may be salient to reducing poor mental health outcomes among Black adults. To address this gap, we will use quantitative data from Black adults residing in Milwaukee, WI who participated in the Midlife in the United States (MIDUS) study (n=1489 combined across waves) and collect qualitative data from Black adults to contextualize the quantitative findings and develop potential intervention strategies. Specifically, we will develop and assess the measurement properties of a multidimensional social connectedness indicator constructed from existing items assessed in MIDUS (e.g., social integration, religious/church-based social support, and social cohesion) (AIM 1a). Then we will test the associations between neighborhood- and individual-level social connectedness with three mental health outcomes (e.g., Kessler-6 psychological distress, MASQ general distress-depressive symptoms, and DSM-III-R major depression) (AIM 1b). To better understand how social connectedness influences mental health, we will estimate the degree to which social isolation and loneliness mediate the association between social connectedness and mental health (AIM 2a) and quantify the extent to which social connectedness buffers associations between racial discrimination and mental health outcomes (AIM 2b). Lastly, in partnership with community stakeholders, we will conduct focus groups to contextualize the quantitative findings and use the first two steps of 6SQuID model to develop potential intervention strategies and targets to address persistent mental health inequities among Black adults (AIM 3). Impact: Investigating the mechanisms undergirding the associations between multidimensional social connectedness and mental health is an important step toward advancing health equity. This study findings will provide a strong evidence-base to inform community-based interventions to modify and leverage social connectedness among Black people as part of a larger ...