The Byron Gilman papers contain a daily account of Gilman's life from September 16, 1861 until September 27, 1864. There is a hiatus between November 30, 1862 and August 1, 1863, during which time Gilman was serving in the Union Army as a volunteer. However, toward the end of his tour of duty, he resumed his journal. This portion of the journal is on notepaper sewn into a booklet; entries before and after his military service are in a hard-bound book. Entries in the diary resume in August 1863 when Gilman, although not yet mustered out, is back in Lynn.

With the exception of accounts of Byron's life in the infantry, the diary consists primarily of descriptions of social evenings with friends, parties and visits, and the entertainments he attended both in the Lynn area and in Boston. Numerous printed programs, newspaper clippings, detailed descriptions and critiques of plays, concerts, lectures, and other curiosities such as acrobats, mesmerists, etc. are inserted in the diary, together with Byron's own evaluations. A photograph of Gilman is also inserted.

In addition to the diaries, the collection includes a document listing the names of soldiers with an account of the articles of clothing they received, a handwritten list of "Articles Worn or Carried about the Person," and "Contents Knapsack". Folder 3 also contains a list of "Massachusetts Militia Company, May 4, 1830 Commanded by Charles Merritt, Leutenant (sic) H. Burchstead Ensign Othis Newhall."