The William S. Leonard papers consist of 39 letters and one receipt covering 1859-1861. Twelve of the letters were written to William by his father, Rev. Levi W. Leonard. They primarily focus on family matters and on the Reverend's declining health and poor financial state. Rev. Leonard seemed to be editing books and a newsletter at this time, and had become a strong supporter of the Republican Party. In a letter of March 4, 1861, he wrote to William that the Republicans had raised the campaign flag to celebrate Lincoln's inauguration, but expressed apprehension about the gathering conflict: “the state of the country is so critical & dangerous, some think it would be more appropriate to toll the bells.”
In her letters to William, Mattie reported her daily activities and expressed her affection for him; she frequently recalled memories of times together and expressed sadness at their separation. In a letter of March 10, 1861, she responded to news of his medical practice (“I hope you have cured that Irish girl’s leg”) and in her March 31 letter, she described wedding plans and a guest list in some detail.
Four letters in the collection were written by a fellow physician and friend of Leonard’s, known only as "Bim.” His letters, in which he addressed Leonard as “Beak,” include discussions of his medical work, such as an outbreak of diphtheria, which he described in a letter of December 10, 1860. The remainder of the letters in the collection come from colleagues, friends, and a cousin and pertain particularly to social engagements, religion, and medicine.