John Hemmings (the last name reflects his spelling) was the son of Elizabeth Hemings and, it was said, Joseph Neilson, one of the white housejoiners hired by Jefferson in the 1770s. Hemmings started his working life as an "out-carpenter," felling trees and hewing logs, building fences and barns, and helping to construct the log slave dwellings on Mulberry Row.
At the age of seventeen he was put to work under a succession of skilled white woodworkers hired by Jefferson to enlarge the main house. Hemmings learned to make wheels and fine mahogany furniture, and to use an elaborate set of planes to create decorative interior moldings. He was principal assistant to James Dinsmore, the Irish joiner responsible for most of the elegant woodwork in the Monticello house.
Overseer Edmund Bacon described Hemmings as "a first-rate workman--a very extra workman. He could make anything that was wanted in woodwork." He made all the wooden parts of a large landau carriage Jefferson designed in 1814.
Jefferson freed John Hemmings in his will, allowing him the tools of his shop. He continued to live at Monticello until 1831, doing occasional work for Jefferson’s family members.