W.E.B. Du Bois's The Philadelphia Negro continues to inform the contemporary disciplines of sociology, geography, and criminology. This essay explores how Du Bois's study of the social and geographical organization of Philadelphia's black residents was informed by prison reform discourse of the period. Founded in Philadelphia in 1787, the Pennsylvania Prison Society is among the oldest and most influential prison reform organizations in American history. By reading The Philadelphia Negro alongside Du Bois’s earlier and contemporary writings about the sociology of race as well as some of the principal insights disseminated by the Pennsylvania Prison Society, the essay demonstrates how racial and criminal identities performed in and through space respond to dominant ideologies about race and the institutions that uphold them.