From Thomas Jefferson Encyclopedia
Jefferson's original tombstone is no longer on Jefferson's grave.
The original tombstone was erected in the family graveyard at Monticello in 1833. Since Jefferson's death it suffered damage at the hands of visitors as they chipped off pieces for souvenirs. The owner of Monticello at the time, Uriah Levy, moved it to the home of Thomas Jefferson Randolph where it remained until it was sent to the University of Missouri.
Once it was decided to build a new tombstone, Jefferson's descendants got many requests for the original marker. University of Missouri was one of them. There are a couple of reasons why it went to the University of Missouri. Missouri was a major state in the Louisiana Purchase and the university was the first in that state, and there were many transplanted Virginians in the state. The original tombstone was unveiled at the university on July 4, 1885 and it is now on the Francis Quadrangle. Meanwhile, the tombstone at Monticello is a replica of the original.
Leepson, Marc, Saving Monticello: The Levy Family's Epic Quest to Rescue the House that Jefferson Built. New York: Free Press, 2001.
University of Missouri-Columbia Archives. http://muarchives.missouri.edu/