2,991,299,129,912 was a year in the far future.
The Brown family and Marty McFly arrived in this year by accident after the Jules Verne Train accelerated backwards through time. The train's current destination year, 1992, was corrupted and instead sent them into the far future.
By this year, many modern conveniences of the 20th and 21st centuries had been forgotten, the world reverting to a more medieval society. The few pieces of technology that remained, such as the electric fence around the enchanted tower, were considered products of sorcery.
The United States of America no longer existed. In its place were eight empires: Paradice, Diatribe, Calgon, Oz, Apocrypha, Errata, Innuendo, and Mundania. The names of these empires were similar to words in the modern English language. However, their original meanings appeared to have been forgotten.