Mary Hern (1780-?)  was a slave who worked as a weaver at Monticello.
In May 1807 Thomas Jefferson wrote in his Memorandum Book: "Bought of Randolph Lewis a woman Mary 27. years old, and her two sons William 6. y. old last March and 4. y. old last February. They are the wife and children of Moses, for Â£150." Moses was Moses Hern (1780-after 1832), son of David and Isabel Hern. He had worked in the Monticello nailery as a boy and was now a blacksmith. His wife, Mary, the property of Jefferson's nephew Randolph Lewis, lived six miles away from Monticello; they had what was called an "abroad" marriage. Hern had repeatedly asked Jefferson to purchase his family. Finally, when Lewis was about to remove to Kentucky, Jefferson reluctantly agreed to purchase Mary and their sons William and Davy.
Mary Hern became a weaver in the cloth "factory" at Monticello. She spent her days working at a loom with a flying shuttle, weaving cloth from hemp, cotton, and wool. The fibers were carded and spun by the other enslaved workers in the textile shop. Four boys in their early teens operated a hand-driven carding machine for cotton, while teenaged girls worked at spinning jennies, machines with 24 or 40 spindles each, which could more than triple the production of spinning wheels. Mary Hern made hundreds of yards of coarse cloth for the summer and winter allotments to Monticello's enslaved families. Charts in Jefferson's Farm Book indicate that the length of her working day and thus her daily task changed with the seasons. In the short days of January he expected a weaver to produce 3Â¾ yards of cloth, while in a 14-hour day in June she had to weave 7Â½ yards.
Moses and Mary Hern had at least ten children. In 1819 Jefferson gave Moses Hern to his grandson Thomas Jefferson Randolph and, in 1824, transferred Mary Hern and some of her children from Monticello to Poplar Forest, possibly to reunite husband and wife, as Randolph had apparently placed Moses Hern there. Although the estate sales after Jefferson's death scattered the family, a number of Moses and Mary Hern's descendants are still in this area today and preserve stories of their connection to Monticello.