The second generation of Pokemon began in 1999 with the release of Pokemon Gold and Silver for Game Boy Color. Like the previous generation, an enhanced version titled Pokemon Crystal was later released. The second generation introduced 100 new species of Pokemon, starting with Chikorita and ending with Celebi. The Pokedex totaled 251 Pokemon to collect, train, and battle, set in Johto, inspired by Japan's Kansai region. The Pokemon 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 Pokemon began in 1999 with the release of Pokemon Gold and Silver for Game Boy Color. So, the answer is 1999.