ABSTRACT: Frederick Jackson Turner, premier historian of the frontier and American exceptionalism, wondered late in his career how sectional identities had formed in the United States. Out of all the American sections, the Midwest seemed to have no distinct character, serving instead as a miniature model of the entire nation. Turner's professional descendants in the Midwestern History Association have interrogated the region's typicality, noting that it became in the twentieth century a generator of progressive reform movements and a new homeland for diverse groups. Looking back at the region's eighteenth- and nineteenth-century past, particularly within the conceptual framework of Indiana University Press's Trans-Appalachian Frontier series (1996–2018), lets historians determine when the Midwest separated from its parent region, the "old" West, which included the Deep South. The territories between the Appalachians and the Missouri River initially shared many features: a large and adaptive Native American population, a commitment among white settlers to commercial agriculture and land speculation, and attractiveness to utopian experimenters. The Midwest separated from this larger region after 1865, when formerly enslaved Black people moved to the midwestern states from the white-supremacist South, immigrants reshaped the social landscape of midwestern cities, and regional authors and artists began constructing a midwestern stereotype in order to critique and demystify it.