Consists of drafts of both individual works and full-length books and book projects by John Ennis in various stages of completion, along with proofs, poem lists, notebooks and loose notes, source materials, research, photographs, cover designs, publicity materials, reviews, correspondence, and press clippings related to Ennis's writings. While the vast majority of materials relate to his poetry, both published and unpublished, a smaller number pertain to musical works created in collaboration with composer Eric Sweeney for which Ennis composed lyrics, drafts of unpublished short stories from the 1970s, and Ennis's 1997 PhD thesis on the use of myth and archetypes in his own poetry.

Draft materials exist for all nineteen of Ennis's books of poetry published in print from 1976 to 2016, as well as for an additional poetry collection he published online, three early book-length collections, several of which are annotated by his mentor Seán Lucy, and three more recent collections, marked "future," that were unpublished at the time the papers arrived at the library. Drafts and related materials that were maintained together by the author and discernibly related to a specific book project are arranged by poetry collection. Drafts of single poems that were not clearly filed with materials for a specific book project are arranged by individual poem, though there may be some overlap in content between the two organizational schemes. While materials arranged by poetry collection generally include a full range of draft, editorial, and publicity materials, often including drafts of individual poems; materials arranged by individual poem consist only of various drafts of a poem, sometimes accompanied by a related clipping or page of notes. There is also a small group of general poetry notebooks and notes that contain drafts of miscellaneous poems and other writings. Researchers interested in Ennis's poetry should also note that poems Ennis wrote while working on a specific book project were sometimes ultimately published in a later book; as a result, drafts of poems published in a later book may sometimes be found with files for an earlier book.

Ennis's writings, which are often heavily revised, are also frequently accompanied by source materials, such as the newspaper clippings, magazines, pamphlets, maps, and brochures that provided both inspiration and factual details for his poems. His extensive notes also regularly include his own personal analysis of his writing, and his poem lists shed light on his process for assembling collections of poems for publication.