This collection contains the personal records of Robert S. Rantoul, including correspondence, financial records, photos and mementos of his children, and news clippings related to his life. It also contains a significant amount of records relating to his professional positions as both the Mayor of Salem and the President of the Essex Institute. The collection is arranged into three series.

Series I. Personal and Biographical Papers contains records documenting Rantoul's personal and early professional life. Included in this series are certificates he received for various legal and political accomplishments, correspondence regarding his life and early work, and mementos of his two eldest daughters Edith and Margaret. Also included are financial records pertaining to his early work as a lawyer and Collector of the Port of Salem, as well as household finances and records pertaining specifically to his in-laws, the Neal's. Rantoul oversaw many legal and financial dealings for the Neal's and was inheritor to his father-in-law's will. Finally, the series contains a folder of Rantoul's personal effects, including early poetry transcriptions, a notebook documenting his trip to Germany for the Centennial, and a hand-drawn map of Salem, as well as a folder of news clippings pertaining both to Rantoul's life and his personal interests.

Series II. Mayor of Salem Papers documents Rantoul's life during his term as Salem's Mayor from 1890-1893. The series contains a large amount of correspondence dealing with Rantoul's professional duties as Mayor, and a folder of politically-themed speeches and writings that he delivered while in the Mayor's office or in the years of his political activity leading up to his election. Included in these speeches are Mayor's Addresses, which document the issues of the day such as water supply, expansion of railways and roads, employment, and crime.

Series III. Essex Institute Papers contains records pertaining to Rantoul's personal and professional affiliation with the Essex Institute, from his early days as a member and researcher through his years as President and later as nominal head of the organization. The series contains a wealth of correspondence addressed both to and from Rantoul as he addressed research requests, sought information or materials from others, and liaised with libraries and historical societies. Additionally, the series documents a number of the pamphlets and essays that Rantoul published as a result of his association with the Essex Institute, including notable works on the Woodbury family genealogy and the first cotton mill in the United States. Supplementing these is a folder of reports and speeches that Rantoul gave on various historical and current topics based on his research at the Institute, some of which were later reproduced in local newspapers or sent to other historians. Finally, this series contains a folder of transcriptions copied either by or for Rantoul from Essex Institute materials and other related historical records for the purposes of research. These handwritten or typed copies clearly address a number of different research interest and projects, but are all undated and detached from their original context.