Jill Jonnes' (1952-) research notes for Conquering Gotham consist almost entirely of photocopies of letters, reports, newspaper articles, and extracts from books, most of which are highlighted or marked by the author. There are also some notes in the author's hand, noting various research leads and to do lists.

The photocopies are taken from mainstream newspapers and magazines, scholarly monographs and memoirs, and from the main actors' business and personal papers, especially A. J. Cassatt (1839-1906), Samuel Rea (1855-1929), Charles F. McKim (1847-1909), William H. Baldwin (1863-1905), James M. Forgie (1868-1958), and Henry Clay Frick (1849-1919). There are extensive extracts from the minutes of the Board of Engineers for the project. While the emphasis is on the technical and political problems faced in building the tunnels and station, there is also considerable background material on Cassatt and Rea's lives and families in particular.

The records were donated to the Hagley Museum and Library to complement Hagley's collections of original material on the Penn Station project. Some items, such as extracts from books in Hagley's collections and newspaper extracts giving background information such as prices and popular events of the day, have been discarded. The rest is arranged according to the author's own system.