There IS Thimerosal in the TetanusToxoid. I went to the link you posted and clicked on the "Tetanus Toxoid Adsorbed USP" name, which took me to a material safety data sheet explaining how the tetanus vaccine is made.

If you read through the list, you'll see that Aluminum, Formaldehyde, and Thimerosal are all in the final vaccine. They indicate that each 5ml dose contains (supposedly not more than) 0.25mg of aluminum and 0.02% (or perhaps less) of formaldehyde. However, I'm not sure how the percentage of formaldehyde is calculated so I don't know how much formaldehyde is actually contained in the final solution.

You'll also read that Thimerosal is used as a preservative in the final solution. In fact, near the end of the sheet under Contraindications, it reads "Hypersensitivity to any component of the vaccine, including Thimerosal, a mercury derivative, is a contraindication for further use of the vaccine."

Also, animals studies indicates that the combination of aluminum and mercury is much more toxic than either substance alone.