Webster's describes a polymath as "a person of encyclopedic learning" "from Greek polymathes 'having learned much, knowing much,' from polys 'much' and root of manthanein 'to learn.'"
We also call these people universal geniuses and Renaissance Men. Granted, the Renaissance has been over for about 400 years, but there still must be Renaissance men (or women!) out there, right?
Wikipedia says no. By their definition (a person of exceptional ["profound"] learning in a variety of subjects) the most recent polymath died in December of 1937.
It seems a shame that we don't have at least a couple rattling around among the 7 billion folks we have here on earth. They were pretty thick on the ground in the late 1400s. Now we're stuck with the poet/scientist or philosopher/astronomer. If only Carl Sagan had learned ancient Greek and classical guitar....