This thesis examines the construction and functions of intellectual disability in the modernist literature of the American South from 1925-1940. The period saw a remarkable proliferation of intellectually disabled figures in various guises. These include William Faulkner's Benjy in The Sound and the Fury which has become one of the most analysed 'idiots' in all literature. However, the wider trend of which he is a part has largely lacked critical attention. Furthermore, the connections between this regional literary trend and the prominence of the eugenic movement in the era have been unexplored. This thesis questions why intellectual disability was so important to Southern writers in particular, and why it appears so frequently in their works. The thesis also examines the extent to which Southern writers incorporated eugenic ideas into their representations and how authors reinforced or challenged contemporary ideas regarding intellectual disability. The thesis offers detailed close readings from a selection of southern writers’ works contextualised with primary and secondary historical source material to adequately trace the period’s social, scientific and aesthetic models of intelligence and intellectual disability. The thesis argues that intellectual disability and eugenics were integral to the ways in which southern writers represented their region, not only in negotating regional and national anxiety regarding southern intelligence, but also acting as a crucial vehicle through which these authors examined the South's uneasy and peripheral relationship with modernity. The thesis adds to a growing understanding of the cultural significance of intellectual disability and the eugenic movement and shows how southern modernists' depictions of intellectual disability were linked to and can illuminate understandings of regional and national debates in the period about intelligence, inheritance, disability, family, community, and modernity.