Abstract: Papers, 1858, 1907-1978, consisting primarily of correspondence and manuscripts of published and unpublished works, of August Derleth, one of Wisconsin's most prominent and prolific writers. Derleth spent almost his entire life in the small Wisconsin town of Sauk City and wrote about its history and its personalities in his Sac Prairie Saga, a nearly fifty-volume sequence of novels, journals, lyric poems, short stories, and miscellaneous prose which comprises one of the major works of American regional literature. Derleth was also a devotee of Howard Phillips Lovecraft, the master of twentieth century weird fantasy, and a major contributor to the “Cthulhu Mythos,” a body of supernatural and science fiction works originated by Lovecraft.