The diary, a single volume comprised of approximately 100 handwritten pages, is inscribed "Diary of Wm E. Potter/Monday Sept. 5, 1859." The first page of the diary contains what appears to be grades most likely from his final year at Harvard. The last page contains subjects for prize debates. The diary itself begins with Sept. 5, 1859 and concludes on June 28, 1862. There are entries for every day between September 1859 and mid-July 1861. Thereafter are occasional periods when weeks and entire months are combined into a single entry.

The diary consists of Potter's days at Harvard (Sept. 5, 1859 to Jan. 8, 1861), a law practice commencing on Feb 4, 1861, his entry into Princeton (Aug. 14, 1861) and his final entry, "Enlisted," on June 28th, 1862.

Many of the entries indicate Potter's simple day-to-day activities. There are lengthy descriptions and comments on Potter's professors including Russell Lowell at Harvard and Lyman Atwater at Princeton.

Potter also provides thoughtful comments on the public figures and events of this period. Of interest is how abolitionist, secession, and war events begin to take up a greater portion of Potter's entries, especially after the election of Lincoln in November 1860. In addition to the entries describing Lincoln's election and inauguration, there are descriptions of the Women's Rights Convention in Boston in 1860, speeches by Edward Everett, secessionist William Lowndes Yancey of Alabama, abolitionists Wendell Phillips and William Lloyd Garrison, Lincoln's appearance and speeches in Trenton and Philadelphia, the surrender of Fort Sumter, the Battle of Bull Run, the "pumping" (dunking) of Princeton students favoring secession, and the fall of Fort Donelson. However, after Potter's religious awakening on February 28, 1862, little note is made of war events. The momentous battles of Shiloh, Williamsburg and Seven Pines are not even mentioned.