<p>Multiracial populations increased faster than any single race in the most recent U.S. census. However, we know little about how this demographic shift might impact the political and racial attitudes of monoracial Americans. This paper addresses this question by examining how learning about the proportion of African Americans with Irish ancestry impacts the racial attitudes of white Irish Americans. Experimental data from the largest online survey of Irish Americans reveal that learning about African Americans with Irish ancestry <i>reduces</i> racial prejudice among white Irish Americans who identify with their Irish American identity, and that these effects are mostly driven by Republicans—i.e., those Irish Americans with higher baseline levels of racial prejudice. Open-ended responses highlight the potential for multiracialism to reduce the perceived distance between racial groups and undermine racially essentialist beliefs.</p>