The collection consists, for the most part, of letters written to Young by other astronomers, such as N. M. Paul of the United States Naval Observatory and Leonard Waldo of Harvard, and by clock, astronomical, and scientific instrument manufacturers, including Howard Grubb, Fauth and Co., E. Howard and Co., and Edward Kahler. In addition, there are some drawings of astronomical instruments and a few bank books.

Further accessions include measures (1879) of the polar and equatorial diameters of the planet Mars by Prof. Young at the Observatory of the John C. Green School of Science, Princeton University, and an autograph manuscript with 12 sheets of figures on graph paper from the G. P. Kuiper Scientific Collection. Also included are letters from Simon Newcomb concerning discussions with Stephen H. Emmens in February and March 1897, and two letters from Young to Stephen Alexander discussing equipment for the astronomical observatory to be built on the "Olden lot" on Prospect Ave. in Princeton.