This series consists of correspondence amongst Cowper's circle of family, friends, editors, and others, as well as a few assorted manuscripts. While the majority of the letters are original, there are also some copies. The primary correspondents include Sir John Carr, William Hayley, Lady Hesketh, John Johnson, John Newton, and Samuel Teedon. This series is first organized alphabetically by correspondent, then alphabetically by recipient, and finally chronologically by date. Unidentified manuscripts are located at the end of the series.

Series 1 consists of proposals and surveys compiled by the Office of Occupational Health and Safety in regards to radiation safety measures taken to protect workers and researchers at the Princeton-Pennsylvania Accelerator, a particle research facility that operated on Forrestal Campus from 1957 to 1971.

Consists of the writings of Milton Halsey Thomas, including college writings, biographical information, genealogies, and works on diaries of various individuals.

Consists of manuscripts, both bound and unbound, mostly oversize, and artwork/ephemera housed in a variety of oversize containers.