Except Dudley Do-Right. It debuted as a segment on the Rocky and Bullwinkle cartoon show. The comic strip characters for the rest of the land appeared in print first, yes.I just kind of appreciate how everything in Islands, whether original or not, originated as a book first.
Some lands speak for themselves: Potter, Lost Continent, Seuss, Toon Lagoon, Marvel all derive themselves from a form of literature (novels, legends, picture books, newspaper comics, comic books, respectively).
Others get a little dicey: Jurassic Park was a book first, and King Kong’s first appearance was in the book adaptation of his first movie, hence why he’s in the public domain despite being a relatively recent character.