Consists of poetry and prose manuscripts, letters by and to Leland, and other correspondence. Among the manuscripts in the collection is a notebook, titled "Essays and Extracts from Old Books and Writers" (1841-1843), in which Leland copied extracts from Hobbes, Spinoza, and others, as well as his own essays. Poetry manuscripts include "Educatio Diaboli" (1842 or 1843), "Serenade" (1842), and "Witch Songs" (undated). Several of the letters by Leland were written while he was a student at the College of New Jersey (one gives a very entertaining account of his suspension in 1842); and others refer to the formation of the American Students' Union, a group which fostered social correspondence between the classes of different universities.

The following standard abbreviations, or their variations, are used to identify materials in this collection: ALS = autograph letter signed, AN = autograph note, AMsS = autograph manuscript signed, ADS = autograph document signed.