Ocampa was the inhabited fifth planet orbiting a G-type star. This Delta Quadrant planet was located approximately 50,000 light years from the galactic core and 75,000 light years from the Badlands in the Alpha Quadrant. It was near the Caretaker's array. The Ocampa were native to this world.
Ocampa had all the characteristics of a class-M planet, with the sole exception of the absence of nucleogenic particles which left the planet's atmosphere incapable of producing rain, and turning its surface into a desert without a single river or ocean.
This was not the planet's natural state (in fact, it still had dry riverbeds), but the result of an accident during the exploration of the planet by a group of Nacene ca. 500 Ocampan generations ago. The Ocampa referred to this era as "the Warming". The Nacene took responsibility for their error by constructing a vast underground city, two miles below the surface and protected by security barriers, to give the Ocampa access to the only water left on the planet. The Ocampa were brought to this city by tunnels. They also left behind two members of the exploration team – Suspiria, and an individual who the Ocampa came to know as the Caretaker – to care for the race.
Although short of water, the planet was rich in cormaline deposits. The Kazon-Ogla sect maintained an encampment on the planet's southern continent, near a dry riverbed at the foothills of a range of extinct volcanoes to mine its resources. Jabin was the leader of this encampment in the early 2370s.
In 2371, USS Voyager was transported to the area near Ocampa. Shortly before the Caretaker passed away, it was said that the Ocampa had enough surplus energy to keep the city running for five years. (VOY: "Caretaker", "Before and After")
Background information Edit
Due to the premise of Star Trek: Voyager, the Ocampa homeworld could not regularly be shown as a setting in the series. (Star Trek: Voyager - A Vision of the Future, p. 164) Scenes of the underground Ocampa city were filmed at the Los Angeles Convention Center.  The surface scenes were filmed at the El Mirage Dry Lake Bed. 
According to Star Trek: Star Charts (p. 78), Ocampa (Ocampa V) was classified as a Class H planet. Its capital was Ocampa. Dominant species on this planet was the humanoid Ocampans. In 2378, there were an estimated 230.0 million Ocampans living on this world. The planet's surface was devasted by the Nacene in the 14th century.
According to Star Trek: Star Charts (pp. 13 & 82) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the primary for the Ocampa system was a G-class star. This system was located near the Vaadwaur subspace corridors. Voyager was at this system on stardate 48317.
According to StarTrek.com, the Ocampa planet's star was named Ocampa.
The Star Trek Encyclopedia (4th ed., vol. 2, p. 99) located Ocampa in the Ocampa system.