This paper investigates William Carlos Williams’s In the American Grain (1925), a collection of essays on American history, in which the poet argues that American Puritanism and its Eurocentric worldview play a most crucial role in attempting to stabilize a unitary notion of American cultural identity. Reading Williams’s essays through the critical lens of Friedrich Nietzsche’s philosophy, this study seeks to explore his development of an anti-Puritan stance toward a locality-based literary practice. Ultimately, Williams’s transatlantic historical imaginary is read here as corresponding to his own drive to promote a life-affirming Dionysian (Nietzschean) poetics, a poetics grounded in the direct experience of local cultures.