As this site notes,
The Robert J. Wickenheiser Collection of John Milton at the University of South Carolina is one of the world’s largest collections of Milton and Miltoniana.
Robert J. Wickenheiser started his Milton collection as a graduate student at the University of Minnesota in the late 1960s. Later, as a faculty member at Princeton, he began focusing on illustrated Milton, and he established friendships with many of the finest antiquarian book dealers on both sides of the Atlantic. In the years that followed, the Wickenheiser Collection has grown beyond six thousand volumes, including more than sixty seventeenth-century editions of Milton’s writings and significant holdings of seventeenth-century Miltoniana. The special focus on illustrated editions makes this arguably the most comprehensive collection of published Milton illustration anywhere—from the first illustrated edition of Paradise Lost (1688) through all the major illustrators that follow, particularly John Martin (1789–1854) and Gustave Doré (1832–1883), and including also original drawings by various other artists, known and unknown. The collection’s eighteenth-, nineteenth-, and twentieth-century editions record Milton’s continuing impact, while expansive holdings of Milton biography, scholarship, and criticism document the growth of knowledge about the poet’s life, writings, and influence.