This collection contains material relating to his legal affairs, medical publications, receipts for books purchased, and information on botany. Important correspondents include Edward H. Clarke, George Mifflin Dallas, Samuel David Gross, and Joseph Henry. There is also family history in these papers.

These are primarily letters, with some receipts for medical services rendered included. They relate to the general social and intellectural life of Philadelphia and to publications on medical topics. Many of the letters are introductions to Europeans when Pennock first visited there. Letters dated post-1867 are to relatives and colleagues (?).