<jats:p> The spatial patterning of present-day racial bias in Southern states is predicted by the prevalence of slavery in 1860 and the structural inequalities that followed. Here we extend the investigation of the historical roots of implicit bias to areas outside the South by tracing the Great Migration of Black southerners to Northern and Western states. We found that the proportion of Black residents in each county ( N = 1,981 counties) during the years of the Great Migration (1900–1950) was significantly associated with greater implicit bias among White residents today. The association was statistically explained by measures of structural inequalities. Results parallel the pattern seen in Southern states but reflect population changes that occurred decades later as cities reacted to larger Black populations. These findings suggest that implicit biases reflect structural inequalities and the historical conditions that produced them. </jats:p>
