In the years since 2010, themes of mental illness on the musical theater stage have increased dramatically, most notably with the Broadway premiere of Dear Evan Hansen in 2016, which quickly became a popular and critical success, winning six Tony Awards the following season. Despite scope and reach of the modern American musical, relatively little musicological scholarship has explored this area, and of that literature, even less has examined contemporary musicals. In this thesis, I will begin to fill this gap in the literature through the application of emerging critical musicological lenses to modern musical theater, both on and off Broadway. This thesis puts forth a set of representational models to explore how mentally ill characters are represented in contemporary American musical theater. Through six case studies of twenty-first century shows employing these models, this thesis examines how these models intersect with narrative critiques and theories put forth by disability studies scholarship to analyze the representations of mentally ill characters onstage. I examine the shows Next to Normal, Be More Chill, In the Green, Preludes, Dear Evan Hansen, and Bandstand to analyze how the internal experience of mental illness is externalized and shown onstage in each of these shows, evaluate which underlying narratives and ideas about mental illness that these representational models contain, and investigate how ideas from disability studies scholarship can illuminate some of the strengths, weaknesses, and failures of these shows in their portrayal of mental illness. Although this thesis relies extensively on ideas, language, and scholarship from disability studies, it is not a disability studies thesis; rather it will demonstrate how scholarly lenses provided by disability studies can be fruitfully applied to musical and theatrical representations of mental illness. In addition to touching on themes of genre, characterization and narrative theory, therapy and treatment for mental illness, and modern marketability of musical theater, this thesis demonstrates that the theories from disability studies scholarship can be fruitfully applied to other depictions of non-normativity, such as mental illness.