From Bulbapedia, the community-driven Pokémon encyclopedia.
A Regional Pokédex is a Pokédex order specific to a certain region of the Pokémon world. None of the regional Pokédexes yet released chronicle all Pokémon known; instead they chronicle those Pokémon native to the region, starting with the Grass-type starter Pokémon, and followed by its evolutions, the Fire-type starter and its evolutions, and the Water-type starter and its evolutions, then continuing through the rest of the Pokémon native to the region. Legendary Pokémon of the region are typically placed near the end, while the very last spot or two are occupied by special Pokémon not normally encountered.
A regional Pokédex will often place newly-released evolutions and pre-evolutions near their base form, no matter how much distance is between them in the National Pokédex. For example, in the National Dex, Scyther falls at #123, with its evolution Scizor at #212. In the Johto region's Pokédex, however, they are #110 and #111, respectively. Capturing all Pokémon in a regional Pokédex will cause the Game Freak developers in-game to award the player with a diploma in Generation I, Generation II, and Generation III. Completing the National Dex awards another diploma in Generation III. In Generation IV, seeing every Pokémon in the Sinnoh region's Pokédex allows the player to receive the National Dex from Professor Oak.
So far, however, only the Sinnoh region's Pokédex does not naturally include all of the new Pokémon released in that generation. The reasons for this are unknown, as many Pokémon numbered as low as 82 in the National Dex have evolutions in the 460's, and neither they nor the new evolution are included in the regional numbering system. Still other Pokémon unrelated to Pokémon from previous generations are numbered as high as 493 in the National Pokédex, and yet do not appear in the Sinnoh regional Dex.
The Pokédex order for the four main regions of the Pokémon world are as follows:
The National Dex, which catalogs every Pokémon currently known, is as follows:
In the spin-off game, Pokémon Ranger, Pokémon information is stored in the Browser, which acts as the Pokédex for Fiore. It is as follows:
In Pokémon Colosseum and Pokémon XD, the Strategy Memo acts as a Pokédex for Orre, listing Pokémon alphabetically.