Danny DeVito reprised the voice of The Lorax for the Spanish, Russian, Italian, and German dubbed versions.
The characters of Ted and Audrey are named after Dr. Seuss (whose real name was Theodor Seuss Geisel) and his second wife Audrey Geisel.
Dr. Seuss' widow Audrey Geisel ended up loving what Illumination Entertainment had done so much, that she gave the rights to them to continue making films based on the books.
Unlike the original book, the Once-ler is shown fully in the story as a human. Executive producer Christopher Meledandri said of the change, "The minute you make the Once-ler a monster, you allow the audience to interpret that the problem is caused by somebody different from me, and it ceases to be a story that is about all of us. Then it's a story about, 'Oh, I see, the person who led us into the predicament is not a person. It's somebody very, very different.' And so it takes you off the hook."
The original name of the town in the movie is Greenville (as can be seen in the scene where the Once-ler is selling his thneeds in the town center, "Greenville Circle") before the commercial success of the product changed the name to Thneedville.