The Edgar Knapp Letters span the years 1862-1864 and are comprised of 40 letters received by Edgar Knapp while he was working as a hospital steward at the U.S. military hospital in Annapolis, Maryland. They are divided into Family Correspondence and Hospital Correspondence. The collection also contains two invitations to Masonic functions in Baltimore, Baltimore Commandery No. 2.

The Family Correspondence series date from 1862 to 1863. It contains 16 letters from Edgar Knapp's brother H. Knapp and one from his sister, both of whom were living in Adrian, Michigan, during the war. Like Edgar, H. Knapp was a medical man. He avidly followed war news and related political events and kept Edgar informed about work and family life in Adrian. Both H. Knapp and his sister were civilian supporters of the Union who did not (during this correspondence) support radical abolitionists. H. Knapp is an unusually capable correspondent who animates every topic he discusses, from the family's horses (e.g. "He is black (and) sleek as a mole...tough as a knob, got a good swingel (and) bollox.," to the feared loss of their brother Randolph at Gettysburg. Two letters relay news from the front 16 and 17 July: "Ran went into Battle of the 3d July (and) charged on the left flank of Genl Lee, where they had the Infantry to deal with." Additional details extend over three closely written pages.

Hospital Correspondence contains letters Knapp received from soldiers for whom he was responsible when they were recuperating in Annapolis. It also includes letters from deceased soldiers' parents, who wrote to Knapp requesting that he send specified personal effects, their son's body, or information regarding their child's final days. Letters in this series date from 1862 to 1864. Together with his letters from home, in which the battlefield loss of a brother figures prominently, this correspondence provides insight into the news and daily concerns that passed through the mind of a military hospital steward during the Civil War.