See his Selected Papers (comp. with a biography by F. B. Rogers, 1965); biographies by F. H. Garrison (1915) and H. M. Lydenberg (1924).
The Surgeon General's library that he developed later became the core of the National Library of Medicine. During his time as Director of the Library of the SGO, 1865-1895, he was responsible for the creation of both the Index Medicus (1879) and the Index Catalogue of the Surgeon General's Office (1880).
He was also for some years professor of hygiene in the University of Pennsylvania. He is also credited with designing the original buildings of Johns Hopkins Hospital, which opened in 1889. The building with the hospital's trademark dome was subsequently named for Billings.
Dr. Billings received an Honorary Fellowship of the Royal College of Surgeons in Ireland in 1892.
After he left the Surgeon General's Office he united the libraries of New York to form the New York Public Library and it was Billings who inspired Andrew Carnegie to provide funds for the construction of sixty-five branch libraries throughout New York and 2509 libraries in cities and towns across North America and Britain.
Dr. Billings was the senior editor of books reporting the work of the Committee of Fifty to Investigate the Liquor Problem in the early 1900s. The Committee researched the activities and publications of the Department of Scientific Temperance Instruction of the Woman's Christian Temperance Union (WCTU).
Billings died in New York City in 1913, aged 74.