Structural racism has increasingly been implicated as a root cause of racial disparities in health and well-being. Specifically, areas where White Americans hold more negative attitudes toward Black Americans have been associated with both anti-Black discrimination and poorer Black physical and mental health. However, previous research has relied on cross-sectional designs and has neglected the potential effects of Black community-level attitudes on mental health. We hypothesized that higher aggregate pro-White bias among White Americans would be associated with higher implicit out-group preference among Black residents living in the same communities, above and beyond the effects of traditional measures of structural racism, and that greater exposure to White residents would strengthen the relationship between White attitudes and Black out-group preference. We further expected that Black out-group preference would predict detrimental Black mental health outcomes. Drawing upon data from Project Implicit, the US Census Bureau, and the Behavioral Risk Factor Surveillance System, the current study utilized a series of two-level autoregressive models to test potential associations between changes in White community-level attitudes and Black implicit bias. County-level bias scores were post-stratified by age and divided into six time periods from 2008-2019. Results indicated that increases in county-level White in-group preference were associated with more negative implicit out-group attitudes among Black Americans. There was no interaction between regional White bias and out-group contact, and no evidence that aversive racism (high implicit, low explicit bias among White Americans) predicted Black Americans’ implicit attitudes. Sensitivity analyses supported the robustness of the associations – White implicit and explicit bias predicted Black implicit bias after controlling for traditional measures of structural racism (Black unemployment, Black educational attainment, and Black incarceration rates) and in areas with differing numbers of Black respondents. With respect to mental health, increases in regional Black out-group preference predicted a higher number of poor mental health days among Black residents, but the relationship was no longer significant after accounting for White Americans’ regional implicit bias. Our results suggest that White Americans’ community-level bias, particularly implicit bias, may exert unique effects on Black racial attitudes and psychological well-being, potentially contributing to intergroup polarization and diminished mental health.