He was in debt so he couldn’t have freed all of his slaves. The ones he freed were Sally Hemings’ children—but Sally herself was not freed. One of her sons, Madison Hemings, was living in Ohio in 1870. The census taker wrote in the margin next to his name “This man is the son of Thomas Jefferson”—obviously that is what Madison had told him.
After Jefferson’s death, Martha Randolph (TJs daughter) placed Sally Hemmings on her “own time” (retired from work)
A little later, Sally was allowed to leave Monticello. She moved in with two of her sons that lived near Charlottesville. In the 1830 census, she and both of her sons were listed as white.