I think Sequoia might be the single most confusing term in Calfornia for much of this reason. The word is used 3 different times to Identify public land.
The Sequoia National Park is where the biggest of the big trees are and is only located in a relatively small area of the mountains east an area from about Fresno to Exeter.
The Sequoia National Monument is a relative newcomer, that was either created or greatly expanded in the mid-90s (I can't remember the exact details). This area extends to a small area north of the national park and a larger area through the mountains to the south that runs about as far south as points east of Porterville. There are still some real nice areas of Giant Trees here, although they aren't as big or great in numbers as in the National Park. However, it is a nice alternative if you want to enjoy these massive trees in an area with a little less tourist traffic.
The Sequoia National Forest pretty much encompasses all the area that isn't in the National Park or National Monument. Especially in the National Monument, you might not even known when you are going between the areas. This area extends almost as far south as Bakersfield, but despite the Sequoia name, you won't find much for Giant Trees here.