Racial segregation is a pernicious feature of life across America. Urban economists and economic historians have studied the forces behind residential segregation, zoning, and housing inequity (e.g., Boustan, 2011; Logan and Parman, 2017a,b). This paper explores another historically pervasive yet less-known institution for racial exclusion: the sundown town. In this paper, we first document the spread of sundown towns outside the South, giving rise to what Loewen (2005) termed a “Great Retreat” of Blacks from the U.S. interior. We then relate this pervasive racial exclusion to the Southern white diaspora (Gregory, 2005), rooted in the historical migration of Southern whites across the country following the Civil War (see Bazzi et al., 2021; Dippel, 2005). Lastly, we connect the presence of the Ku Klux Klan and lynchings to sundown towns, as mechanisms via which whites, both Southern and non-Southern, enforced racial exclusion.