Gravity Falls
History
Up until the Transcendence, the history of Gravity Falls can be assumed to be fairly identical to that of the town from the official canon.
The source of Gravity Falls's weirdness stemmed from an alternate dimension, or the Mindscape, which was leaking into our world. Pre-transcendance, Bill Cipher used Gravity Falls as a testing ground of sorts. The merging of Gravity falls with the Mindscape would serve as the prelude to the Transcendence.
After the Transcendence, Gravity Falls would go down in history as being the origin of the event.
Residents
Candy
Grenda
Pacifica
Mabel
Dipper
Wendy
Henry
Willow
Акация
Hank
Alice
Mike
Places
The Mystery Shack - Converted into a library of the supernatural
Candy's weapon shop - Sells both mundane and magically enhanced weaponry
Grenda's rescue/adoption center - Deals mostly with supernatural creatures
Post Transcendence
After the Transcendence took place, Gravity Falls became a much more notable town. Being the epicenter of the global change, researchers, cultists, and tourists began to flock to the small town. Despite all the attention it got, it never became anything more than a small Oregon town where interested people would find themselves headed.
It has special importance to Dipper in that the residents, despite his transformation, don't treat him differently from when he was human. For as long as that lasted, it played about as important a role as Mabel in keeping him grounded.