Isaac Jefferson, also likely known as Isaac Granger (c. 1775 – 1846) was a slave owned by US President Thomas Jefferson who crafted and repaired products as a tinsmith, blacksmith, and nailer at Jefferson's Monticello estate.

Although Thomas Jefferson gave Isaac and his family to his daughter Maria and her husband John Wayles Eppes in 1797 as a wedding gift, Isaac Jefferson/Granger appeared to gain his freedom by 1822 according to his memoir. In the 1840 census, he was recorded as Isaac Granger, a free man working in Petersburg, Virginia. Rev. Charles Campbell interviewed him there and published his memoir under the name of Isaac Jefferson in 1847 a year after Isaac's death. Granger/Jefferson describes Thomas Jefferson as a master and his part in the lives of his slaves.

Born into slavery in 1775, Isaac was the fourth son of Ursula Granger and Great George (a son Archy died in early childhood before Isaac was born). His father rose in the hierarchy from foreman of labor to become overseer of Monticello in 1797, the only slave to reach that position under Thomas Jefferson. He was paid an annual wage of £20. In 1773, Jefferson had purchased Isaac's mother Ursula and she became a highly trusted domestic slave. She served as a pastry cook and laundress, with duties including meat preservation and the bottling of cider. Isaac's older brothers were George and Bagwell.

Isaac spent his childhood on the plantation near his parents. His early tasks included carrying fuel, lighting fires, and opening gates. Because Jefferson took Great George, Ursula, and their family with him to Williamsburg and Richmond when he was elected governor, the boy Isaac witnessed dramatic events during the Revolutionary War. He later recounted vivid memories of 1781, including Benedict Arnold's raid on Richmond and seeing the internment camp for captured slaves at Yorktown.

Probably about 1790 at the age of 15, Isaac began his apprentice training in the metalworking trades. During the George Washington administration, Jefferson took Isaac as part of his household to Philadelphia which was then the nation's capital. He arranged to have the youth apprenticed for several years to a tinsmith, a skilled and valued trade. Isaac Jefferson's account is the only source for this aspect of his working life. He learned to make graters, pepper boxes, and tin cups, about four dozen a day.

After the household's return to Monticello, the Jefferson set up a tin shop. Isaac Granger/Jefferson recalled that it did not succeed economically. Training as a blacksmith under his older brother Little George, Isaac added to his skills. Sometime after 1794, he became a nailer as well, and was assigned to both nail making and smithing.

By 1796, Granger had a wife named Iris and a son Joyce. He was working extra hours in the blacksmith shop to make chain traces, for which Jefferson paid him three pence a pair. According to Jefferson's records, Granger was a most productive nailer. In the first three months of that year, he made 507 pounds of nails in 47 days, wasting the least amount of nail rod in the process. He earned the highest daily return for his master: the equivalent of eighty-five cents a day.

In October 1797, Thomas Jefferson gave Isaac, his wife Iris, and their sons Joyce and Squire to his daughter Maria and John Wayles Eppes as part of their marriage settlement. This was customary practice in those years by planters who had sufficient slave holdings. He also gave the Eppes the 14-year-old slave Betsy Hemmings, who would serve as their children's nurse and became the matriarch of the slave society at the Eppes plantation, Mont Blanco, in Chesterfield County.