The 1864 leather bound, preprinted diary contains two daily entries per page with cash accounts and notes sections in the back of the diary. In 1864, Benjamin M. Peck was the Captain of Company B in the 141st Regiment PA Volunteers. Due to absences, injuries, and illness of other officers he was placed in command of the regiment before being assigned to lead the 1st United States Sharp Shooters. Brigadier General Byron R. Pierce saw fit to place him in charge of the three companies of sharpshooters and he remained in this position until the end of the war. Peck describes battles, skirmishes, picket lines, commands, and other military assignments and engagements in great detail. He notes the various marches and travel routes of his company and records his travels between the Virginia front and his home in Towanda, PA. As part of the Army of the Potomac, Peck recounts the regiments campaign in Virginia and the Siege of Petersburg. He lists his men who were wounded or killed in battle, describes court martial proceedings, and even gives an account of the execution of a Union soldier for desertion. Following the 1864 presidential election he enumerates each candidate's results within the division, which Lincoln won convincingly.

The 1865 leather bound, preprinted, pocket diary contains one entry per day with cash accounts and notes listed in the back of the book. This diary continues with the 141st PA Volunteers camped outside of Petersburg in their winter quarters and continues through the end of the war and Peck's return home. He recounts the fall of Petersburg, the Union pursuit of Lee's Army of Virginia across the state, and Lee's ultimate surrender at Appomattox Court House. Peck was assigned to preside over several court martial proceedings and gives details regarding these proceedings and punishments, which include a botched execution of a Union soldier. As in the first diary, Peck provides an account of the daily movement of Union troops and supplies. He also gives detailed lists of captured soldiers and artillery, as well as Union wounded and casualty records. As the war nears its conclusion Peck was in charge of mustering out soldiers and kept thorough records of the process. He also recounts receiving the news of Presidents Lincoln's assassination and describes the mood of the men upon hearing the President was killed. The entries end in July of 1865 with Peck practicing law in his home town of Towanda, PA.

A transcript of the diary is available as part of the collection.