Kanto
in firered and leafgreen you play in the kanto region
You begin in the Kanto region...fire red takes place in Kanto
Taillow is a 3rd Generation Pokemon or a Hoenn region exclusive Pokemon meaning that Firered version which takes place in the Kanto region cannot capture it. All 3rd Generation Pokemon must be traded to Firered from either Ruby, Sapphire or Emerald.
golden rod city is in the johto region and fire red takes place in the kanto region
kanto
You can't get to the johto region in firered.
The games the you are in Johto, are Gold, Sliver, Crystal, Heartgold, and Soulsliver. Im not sure how you reach the Johto Region, but the only games that take place in it are Pokémon Red, Blue, Yellow, Gold, Silver, and Crystal. Although LeafGreen and FireRed are both remakes of Red and Blue, you can't access Johto in LeafGreen and FireRed. Hope this helped.
The UNOVA Region
They take place in a region called Sinnoh.
kanto
Whirl islands are in the johto region which is not in firered.
You can NEVER go to the Hoenn region in LeafGreen or FireRed. You may trade with Ruby/Sapphire/Emerald, but NO!!!