Claims that Thomas Jefferson fathered the children of Sally Hemings, a slave at Monticello, have received support over the past 35 years from revisionist biographies, DNA testing and other evidence. The claims have also been communicated to the general public through novels, films and other popular media. Both those persuaded by the claims and those critical of them assume that collective memory of Jefferson has been changed importantly, and that a considerable portion of the American public accepts the changes, which also include a new focus on Jefferson’s views and actions regarding slavery more generally. But collective memory at the individual level requires some degree of collective knowledge, and after reviewing the nature of memory of Sally Hemings at the cultural level, we explore the extent to which knowledge and belief about a Jefferson—Hemings liaison and Jefferson’s paternity has spread through the American population. We also consider differences in knowledge by race, education, gender and birth cohort. As part of our investigation, we compare the extent of knowledge of Sally Hemings — and the degree to which it carries hints of uncertainty — with what is true for other names and events from the past, including the name of another woman associated with an even more famous American president.