Using the University of Chicago as a case study, this essay examines the racial foundations of sociological thought during the discipline's rising academic legitimacy and cultural authority, in the rst half of the 20 th century. Much more than critical hindsight, the basic theories and methods developed by the "Chicago School" and Robert Park in particular did not just construct racial categories, but were constructed by national anxieties about racial differences in urbanizing America. From this anxiety emerged a "second wave" of Black social scientists who both offered important and under recognized critiques of the "Chicago School" outlook, while reinforcing its industrial framework of organization and civilization in ways that marked "Black" identity as maladjustment, deviance and dysfunction. By stripping away this overarching sociological framework and resituating the "data" derived from "Black subjects" within its migrant and urban context, this essay ends with thoughts about how Chicago's Black residents theorized themselves, their neighborhoods and the larger world in ways that challenged both White and Black sociological visions.