The Moon is a major setting in the Dark of the Moon series.
The Moon holds a secret in the film. The Autobot Ark rests on it after a destructive origin It was shot down by Decepticons while it's commander, Sentinel Prime, was fleeing Cybertron with the Pillars, which supposedly would've won them the Cybertronian War. The Ark's existence on the moon has been covered up by the government since man first landed on the Moon.
Earth's Moon is also seen in the Dark of the Moon film when Buzz Aldrin and Neil Armstrong make their famous journey there in July of 1969, which housed the Apollo 11 mission. While the two astronauts are on the Moon, they discover the crashlanded Ark, which they explore and take several samples of it. Afterwards, they head back to Earth to tell the government of their discovery.
In June of 2011, Optimus Prime discovers a fuel cell from the Ark at Chernobyl. Since he recognized it, he knew that the Autobots' bond with the humans had been severed. He interrogated Charlotte Mearing about the fuel cell being in humans' hands without the Autobots knowing. This lead into a conversation, which Buzz Aldrin himself and several of NASA's Administrators participated in. It came to the conclusion that Optimus realizes that the ship was truly the Ark, and that its captain, Sentinel himself, had been lost ever since the war on Cybertron. Due to this realization, him and Ratchet travel there on the Xantium. Once they arrive, they find four of Sentinel's Pillars and the Control Pillar, as well as a stasis locked Sentinel Prime, who they bring back to Earth and resurrect.
Later in the film, Sentinel betrays the Autobots and kills Ironhide before wrecking the NEST base and heading to the National Mall in Washington D.C. There, with Megatron and Starscream supervising, he spreads the Pillars out over the Reflecting Pool. This sets up a Space Bridge that allowed the stasis-locked Decepticons and stranded Decepticon ships on the Moon come to Earth.
Even with the film's title relating to the Moon, it is not seen again in the film.