The second generation of Pokémon began in 1999 with the release of Pokémon Gold and Silver for Game Boy Color. Like the previous generation, an enhanced version titled Pokémon Crystal was later released. The second generation introduced 100 new species of Pokémon, starting with Chikorita and ending with Celebi. The Pokédex totaled 251 Pokémon to collect, train, and battle, set in Johto, inspired by Japan's Kansai region. The Pokémon mini is a handheld game console released in November 2001 in North America, December 2001 in Japan, and 2002 in Europe.

When did the second generation of pokemon come out? Let's have some stream of consciousness first.
To answer this question, we should know that: The second generation of Pokémon began in 1999 with the release of Pokémon Gold and Silver for Game Boy Color. So, the answer is 1999.