Lydia R. Baldwin was born in Southampton, Massachusetts. Her father was Ezekiel Baldwin. She entered Mount Holyoke Female Seminary in 1843 and graduated in 1845. She worked as a teacher in Easthampton, Northampton, Southampton, and Westfield, Massachusetts, and then married David B. Phelps in 1849. They had three sons and a daughter. She died in Southampton in 1872.

The Lydia R. Baldwin Phelps Papers consist of correspondence, compositions, a certificate, and a biographical note. The papers chiefly reflect her activities as a student at Mount Holyoke Female Seminary in South Hadley, Massachusetts from 1843-1845. In six letters to family members she discusses her studies, domestic work, daily schedule, expenses for the purchase of books, and the food, regulations and religious life at the school. She notes the occurrences of such illnesses as scarlet fever, smallpox, and "lung fever" (tuberculosis) among students, teachers and area residents and discusses her dental problems, Several of the letters mention Mary Lyon's enthusiasm for missionary work and funds raised by teachers and students to support this effort; she also comments on missionary meetings at the Seminary including one where a student who was the daughter of missionaries appeared in native costume. Letters written in June 1844 and July 1845 describe Mountain Day expeditions, one of them featuring lectures by Edward Hitchcock and a number of other Amherst College professors. An additional letter is from Martha Lyman regarding her possible enrollment in the Seminary. Fourteen compositions in the collection reflect English language instruction in writing at the school and concern subjects such as a "Tour to the North Pole," "The Natural Sciences and Mathematics compared," "Popery," and "A Mother's Love." The compositions include some comments by teachers and often reflect the importance of religion at Mount Holyoke. These papers also include a certificate from her minister M. E. White attesting to Phelps' good character and a biographical note from about 1872.

This collection is organized into four series:

• Correspondence
• Compositions
• Certificate
• Biographical Information