Here's a breakdown:
* Pokémon TV series: The first episode, "I Choose You!", aired in Japan on April 1, 1997.
* Pokémon books: The first Pokémon book, "Pokémon Red & Blue: The Official Nintendo Player's Guide," was released in September 1998.
So, the TV series actually predates the first Pokémon book by about a year and a half.