Who was the last presidential candidate to have owned slaves?

[minionofmidas]

Your statement is technically untrue. Grant only ever owned one slave, not "slaves" (whom he also manumitted a couple of years after inheriting him, before the outbreak of the Civil War. His wife, otoh, continued to own the slaves she had inherited until 1865. Over whom Grant would have had a considerable measure of day-to-day control even though he had no right to change their status, obviously.) After Grant and for a long time, there were no presidential candidates with southern family connections. Unless there's some among the minor parties - prohibition, socialist, whatever - the answer is, strictly speaking, "Breckinridge and Bell". Or Grant if we modify it to "a slave / slaves".
Though I'm not entirely sure but it seems likely that Woodrow Wilson spent his early childhood as part of a slave-owning family - certainly a very pro-slavery and pro-Confederate family, anyways.