factcheck.org:

We wouldn't make too much of this, though. After all, according to at least some researchers, a common ancestor for all humans now alive may have existed just several thousand years ago. That means you, dear reader, could have a cousinly relationship that may not go all that far back to everyone from Jack Kevorkian to Tina Fey to Hugo Chavez to the woman selling trinkets from a piece of cardboard on a Bangalore street corner.

Barack Obama related to Brad Pitt, 6 U.S. Presidents, Cheney

This family tree stuff has whiskers. I was happily living in Alice Springs, well over a thousand miles from the nearest known relative. Someone dug up the family tree and I'm related to half a dozen people around the Alice. I keep away from Facebook etc for the same reasons. Think I'm safe here though.

It's been said that every US president so far has a distant relationship to the British royal family (don't go asking where I read that, because it was a long time ago and I'm not going to get on ask.com to look). It's probably likely that anyone in the US whose family has been in the country since the colonial days has a connection to one or more presidents and other prominent people. On my maternal side, Thomas Jefferson was a multi-great uncle, and that part of the family also has connections to Ulysses Grant and Robert Fulton. In the 1980s, I moved a thousand miles to take a new job and found myself working with someone who was a multi-great grandson of Fulton's and, therefore, a distant cousin.