For one whole summer vacation, twins Dipper and Mabel Pines are sent to visit their great-unclenote Stan in the valley town of Gravity Falls, Oregon, where he owns the Mystery Shack, a tourist trap operating as "the world's most bizarre museum". Dipper and Mabel's situation worsens (or rather, improves) when Dipper finds a mysterious book, the cover bearing an insignia of a six-fingered hand marked with the number "3". Upon opening it, he discovers that it is a Great Big Book of Everything, explaining the many strange beings, past events, and even federal cover-ups that exist within this town of secrecy — all cut through with an urgent warning: Trust No One!
Thus begins Dipper and Mabel's adventures as they interact with the supernatural world that surrounds them, all while following a Myth Arc where Dipper tries to find the journal's mysterious author.
After the Season 1 finale, the series went on a year-long hiatus. Several mini-series of short films were released over the break to keep fans satisfied. Season 2 premiered on August 1, 2014, a year after Season 1. The series was rebranded as a Disney XD original series, with episodes premiering on that network first before airing later on Disney Channel. In November 2015, Alex Hirsch announced that Season 2 would be the final season, with the Grand Finale airing February 15, 2016, as a one-hour special. Hirsch has since stated he remains open to the idea of continuing the series with additional episodes or specials, and he delivered with the defictionalized book Gravity Falls: Journal 3 and the comic book anthology Gravity Falls: Lost Legends.
A DVD/Blu-ray of the complete series was released on July 24, 2018 from Shout! Factory, making it the first Disney animated series to receive such a release. You can vote for your favorite episode here.
"Bewarb" of spoilers.