The industrialized world is becoming more ethnically diverse. Research in several disciplines has suggested that exposure to racial out-groups may be associated with more positive and more negative intergroup attitudes. Given that U.S. states are often at the center of debate regarding diversity-related public policy, we examined how exposure to out-groups is associated with state-level implicit and explicit race bias among White and Black Americans. We found that larger proportions of Black residents across U.S. states were associated with stronger implicit and explicit in-group bias among both White and Black respondents. State-level bias was predicted by proportions of Black residents even when controlling for (a) state-level demographic control variables (e.g., median income), (b) proportions of non-Black minorities, and © historical membership in the Confederacy. Our results convey the importance of investigating why diversity may not always have the positive impact on intergroup relations that one might hope it to have.