Previous research has documented that the ethnic diversity of where people live predicts implicit biases. More specifically, the extent to which Black people are automatically evaluated less positively than White people (implicit pro-White bias) has been shown to be weaker in more multiethnic areas (Sadler et al., 2021). However, the concept of social dominance orientation, which is the extent to which hierarchies and inequality among social groups are supported (Sidanius et al., 2017), has not been explored in this area of research. The present study investigated whether social dominance orientation, assessed at the county level, mediated or moderated the relationship between ethnic variety and the implicit pro-White bias. The sample (N = 3,654,627) included 67% of White and 11% of Black participants; it was composed of mostly young adults (M = 28.89) and included more women (62%) than men. A total of 791 counties were included in the analyses. The Race Implicit Association Test, administered through Project Implicit, was used to assess the implicit pro-white bias. The social dominance orientation scale was also administered through Project Implicit. 2010 U.S Census data were used to measure the extent to which various ethnic groups were evenly represented at the county level (ethnic variety). Data were analyzed using multiple linear regressions. The results indicated that county-level social dominance orientation partially mediated the relationship between ethnic variety and the implicit pro-White bias. These findings suggest that, as counties become more multiethnic, preferences for inequality and competitiveness among social groups decreases, which may help reduce the extent to which Black people are automatically evaluated less favorably than White people. There was no evidence to suggest that county-level social dominance orientation moderated the relationship between ethnic variety and the implicit pro-white bias. This study gives further insight into one possible mechanism through which the presence of multiple ethnic groups in a context contributes to dismantling the widespread and deeply rooted implicit pro-White bias through the deconstruction of preferences for hierarchical structures in society.