Starting Area
* Rival (Blue): Your main rival, who you battle several times throughout the game.
* Youngster Joey: Your first trainer battle outside of Pallet Town.
Viridian Forest
* Bug Catcher: Multiple encounters.
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Pewter City
* Gym Leader Brock: The first Gym Leader.
* Super Nerd: Outside the gym.
* Youngster: Multiple encounters.
Route 4
* Lass: Multiple encounters.
* Youngster: Multiple encounters.
Route 3
* Youngster: Multiple encounters.
Route 24
* Trainer: Multiple encounters.
Route 25
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Cerulean City
* Gym Leader Misty: The second Gym Leader.
* Sailor: Multiple encounters.
Route 2
* Fisherman: Multiple encounters.
Route 1
* Youngster: Multiple encounters.
Route 5
* Fisherman: Multiple encounters.
* Youngster: Multiple encounters.
Route 6
* Lass: Multiple encounters.
* Youngster: Multiple encounters.
Route 7
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 8
* Lass: Multiple encounters.
* Youngster: Multiple encounters.
Route 9
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Vermilion City
* Gym Leader Lt. Surge: The third Gym Leader.
* Sailor: Multiple encounters.
Route 11
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 12
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 13
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
* Fisherman: Multiple encounters.
Route 14
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 15
* Lass: Multiple encounters.
* Youngster: Multiple encounters.
Route 16
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 17
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
* Fisherman: Multiple encounters.
Route 18
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 19
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 20
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 21
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 22
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Lavender Town
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 23
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Celadon City
* Gym Leader Erika: The fourth Gym Leader.
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
* Super Nerd: Multiple encounters.
* Gentleman: Multiple encounters.
Route 26
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 27
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 28
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Fuchsia City
* Gym Leader Koga: The fifth Gym Leader.
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
* Gentleman: Multiple encounters.
Route 29
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 30
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
* Fisherman: Multiple encounters.
Route 31
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 32
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Cinnabar Island
* Gym Leader Blaine: The sixth Gym Leader.
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 33
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 34
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 35
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 36
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 37
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 38
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 39
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 40
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 41
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Route 42
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
Victory Road
* Youngster: Multiple encounters.
* Lass: Multiple encounters.
* Trainer: Multiple encounters.
Indigo Plateau
* Elite Four Lorelei: First member of the Elite Four.
* Elite Four Bruno: Second member of the Elite Four.
* Elite Four Agatha: Third member of the Elite Four.
* Elite Four Lance: Fourth member of the Elite Four.
* Champion (Rival - Blue): The final battle against your rival.
Important Notes:
* The order of encounters can slightly vary depending on your route choices.
* The number of each trainer type you encounter may vary, but the general types listed are accurate.
* There are also some optional trainers scattered throughout the game.
I hope this helps!