|Born||5 February 1745
|Died||16 September 1819
|Cause of death||Strangulated hernia|
|Resting place||Granary Burying Ground|
|Nationality||American - He was also a known Loyalist to the British.|
|Education||Harvard College, University of Aberdeen|
|Title||Surgeon General of British Forces in North America 1776-1780|
|Spouse(s)||Sarah Jeffries (nee Rhoads) - m.1770 and d. 1780; Hannah Jeffries (nee Hunt) m 1787|
|Children||John Jeffries II, Ann Jeffries|
|Parent(s)||David Jeffries (1714–1784) and Sarah Jaffrey Jeffries (of 13, 3 with Sarah and 10 with Hannah)|
Born in Boston, Jeffries graduated from Harvard College and obtained his medical degree at the University of Aberdeen. He is best known for accompanying Jean-Pierre Blanchard on his 1785 balloon flight across the English Channel. Dr. Jeffries also played a large role in the trial for the Boston Massacre as a witness for the defense. He was the surgeon for Patrick Carr, who was one of the Americans shot during that incident.
Jeffries is also credited with being among America's first weather observers. He began taking daily weather measurements in 1774 in Boston, as well as taking weather observations in a balloon over London in 1784. National Weatherperson's Day is celebrated in his honor on 5 February, his birthday. The Archives and Special Collections at Amherst College holds a collection of his papers, including a letter he dropped from the balloon during his historic flight, considered the oldest piece of airmail in existence.
He lived in England from 1776 to 1790. Despite being named in the Massachusetts Banishment Act, he returned to private practice in Boston, staying there until his death in 1819. His son John Jeffries II (1796-1876) was an ophthalmic surgeon and co-founded the Massachusetts Charitable Eye and Ear Infirmary.
- "MHS Jeffries Family Papers, 1622–1880". Massachusetts Historical Society. Retrieved 28 October 2012.
- Channing 1820, p. 63
- Channing 1820, p. 70
- "The Summary of the Boston Massacre Trial". Boston Massacre Historical Society. Retrieved 28 October 2012.
- "Doctor John Jeffries". CelebrateBoston.com. Retrieved 28 October 2012.
- February 5 is National Weatherperson's Day
- Jeffries Air-Mail Letter Collection.
- Channing, Walter (1820). The New-England Journal of Medicine and Surgery: And Collateral Branches of Science. Volume 9. Wells and Lilly.