This was given to me by our Ped:
http://www.fda.gov/cber/vaccine/thimerosal.htm

Pages 8&9 list the amounts of Thimerosal in different vaccines. What I would do is find out ahead of time which vaccine (Trade name/manufacturer) your pediatrician will use and you can look it up to make sure it's Thimerosal free. And make sure at the visit that they are administering that same one just to be sure.
Rather than love, than money, than fame, give me truth. I sat at a table where were rich food and wine in abundance, and obsequious attendance, but sincerity and truth were not;
and I went away hungry from the inhospitable board.
-Henry David Thoreau