What I’ve read is that the children born to Sally Hemings could have been fathered by anyone of several Jefferson men. It merely suits America hating, race card playing liberals to put forth Thomas Jefferson as the father, so that they can draw a moral equivalency between an esteemed Founding Father and the immoral behavior of Bill Clinton, Barney Frank, et al. The question that black liberals never answer is, “if you are so horrified at America’s history of slavery and Jim Crow, why are you here?” We know the answer to that one.
Madison Hemings was living in Ohio in 1870. The census taker wrote on the census form "This man is the son of Thomas Jefferson." Obviously Madison had told him that--it wasn't supposed to be noted but obviously the census taker couldn't resist writing it down. I've seen the census record on microfilm.
It's actually a Left-wing memetic attack on the language of the Declaration of Independence and the limited-government, anti-Leviathan political tradition that goes back to Jefferson and the Anti-Federalists (who were, by the way, the fathers of the Bill of Rights -- which Alexander Hamilton famously, and somewhat insidiously, denounced).
It stands to reason that totalitarian statists like modern "liberals" and "progs" (so-called: they're all Stalinists, actually) would attack men like Jefferson, who were exponents of the American liberty tradition.
Their lead dog, by the way, has been an Australian journalist with an absolute bloody-eyed thing about Jefferson.