Ariel is a central planet of the Union of Allied Planets. It is home to a major medical centre (named Saint Lucy's) of the Alliance's solar system. The majority of the action of the episode "Ariel" occurs on this planet. Ariel could be named after the moon of Ariel, one of Uranus' moons in the system of "Earth that was," which gets its name from the sprite in William Shakespeare's "The Tempest". The crew of Serenity arrives on this planet for a heist on an advanced medical facility.

Athens is a border planet with at least four moons. One of its moons is Whitefall.

Beaumonde is a fairly wealthy planet, relatively close to certain border worlds. The planet is known to have factories and ranches. The Serenity crew arrives here after their heist on Lilac, to share part of their earnings with the brothers Fanti and Mingo. At the bar called Maidenhead, which was chosen for these dealings, they discover River's Alliance conditioned fighting abilities. This occurs during the Serenity movie. About seven months earlier, the crew was headed for Beaumonde in the episode "Our Mrs. Reynolds". Beaumonde roughly translated from French means "Beautiful World".

Bellerophon is an Alliance moon, home to the wealthy. It has both a large ocean and an empty area of desert climate, complete with canyons, rock and sand. Isis Canyon is pointed out as the most deserted spot on the world. Bellerophon is also the home of Bellerophon Estates, large self-contained estates that float above the ocean waters. Described as "gracious living, ocean views and state-of-the-art security." This is where Durran Haymer lives, a collector of priceless Earth That Was artefacts. Seen in the episode "Trash". The planet is named after a hero in Greek mythology.

Bernadette is a non-terraformed moon near the core worlds whose environmentally-sealed station is used as a staging location for ships of settlers headed for the border planets. The settlers in "Bushwhacked" left from here on their way to Newhall.

Beylix is a small border moon, used for smuggling rendezvous. Mal's war buddy Monty was caught by the Alliance here. Mal refers to it in the episode "Trash". In the role-playing game, Beylix appears to have a permanent cloud cover and dense ice rings.

Boros is a planet with strong Alliance presence. Originally the destination of the travellers picked up by Serenity on Persephone. Mentioned in the episode "Serenity".

Constance is a world where Mal, Zoe and Jayne try a bank heist while Shepherd Book delivers a sermon to act as cover. Seen in the Serenity comic.

Dyton possibly the home planet of Badger. The colony's inhabitants were likely of British origin, since cockney accents appear common among people from Dyton. Referred to by River in the episode "Shindig".

Ezra is a desert moon orbited by Niska's Skyplex. Malcolm Reynolds tries to sell medical supplies here. Named in the script for "War Stories"

Georgia is a gas giant, around which Ezra and Regina orbits.

Greenleaf is an Alliance planet. Located 10 hours away from Jiangyin. [2] Mentioned in "Safe" as a location likely to have medical facilities.

Haven is the home of Shepherd Book, who left the crew during the Serenity comics, and where he resided in the movie. It was also a place of refuge for the Serenity crew.

Heinlein is a gas giant around which Triumph orbits. It may have been named in honour of science fiction author Robert A. Heinlein.

Hera is an Earth-like planet with important significance to the Unification War. Serenity Valley is located here, where the Independent Faction experienced a crushing defeat at the hands of the Alliance. First mentioned in the episode "Serenity". Hera is named after a goddess is Greek Mythology.

Higgins' Moon is a moon where the primary commercial activity is mud farming which is performed by indentured servants called "mudders". The mud is exported offworld and used in the manufacturing of ceramic components. The bulk of the population is impoverished. The moon appears to be owned by a magistrate named Higgins. Jayne became a folk hero to the mudders in the town of Canton due to his role in a botched heist about four years before the time of the Firefly series. The crew visits Higgins' Moon in the episode "Jaynestown."

Ita is a moon in a remote sector. The crew of the S.S. Walden was returning from a salvage mission here before they discovered Serenity's distress signal in the episode "Out of Gas".

Jiangyin is a border planet located 3 weeks away from Persephone, and also nearby Greenleaf. Alliance law is known to be upheld here. The crew of Serenity sells their cattle here in the episode "Safe". The planet is most likely named after a city in China's Jiangsu province along the Yangtze River.

Lilac is a border world probably near Reaver territory. From space it appears to have a lilac colour, which presumably it was named for. The Serenity crew land on Lilac to rob a bank holding an Alliance payroll.

Londinium (sometimes spelled Londinum) is one of the two Major planets. It is inhabited primarily by colonists from the United States and is the location of the Alliance Parliament. Londinium was the Roman name for London.

Miranda is the name of a planet located beyond Reaver territory.  It was home to an Alliance colony with a population of 30 million. The Alliance experimented on the population to find a way to make people more controllable. However the experiments failed: 99.9% of the population became so passive that they essentially lost the will to live. The opposite effect was observed in the remaining 0.1% of the population, who became extremely aggressive and butchered the Alliance scientists in charge of the experiments. This tenth of a percent of the population escaped to become the Reavers. The Alliance tried to cover up what had happened on the planet by creating a story that the colony was lost due to failure of environmental changes caused by the failure of the terraforming to take hold.

Muir a moon where the character Badger was raised.

Newhall is probably a border planet, it was the destination of colonists coming from Bernadette in the episode "Bushwhacked".

Osiris is a wealthy core planet where Simon Tam attended medical school and worked as a trauma surgeon. Mentioned in the episode "Serenity".

Paquin is a location mentioned as having a job for Mal and his crew in the episode "Objects in Space".

Persephone is a civilized planet with heavily stratified societal structure. The Eavesdown Docks are located here, a commercial port and Badger's base of operations. The Serenity crew lands here periodically to resupply and pick up work. Simon and River Tam, as well as Shepherd Book were picked up here in the episode "Serenity". The planet was also the site of a sword fighting duel between Malcolm Reynolds and Atherton Wing in the episode "Shindig". Persephone's name comes from Greek mythology as the name of the "Queen of the Underworld".

Regina is a mining planet, in which everyone is suffering from "Bowden's malady", a degenerative disease. This is where "The Train Job" takes place.

Santo is an unsophisticated planet near Persephone. From space, the planet has a blueish grey colour. Mal and Jayne get into a fight with some slavers here. Seen in the episode "Shindig".

Shadow is where Mal Reynolds was raised on his mother's ranch. The RPG states that it was rendered uninhabitable during the Unification War. "No one lives there. No one can."

Sihnon, together with Londinium, is one of the two major planets. It is inhabited primarily by colonists from China. The planet is highly sophisticated and technologically advanced. It is also Inara Serra's home planet. From space, the planet has a deep red colour. Mentioned in the episode "Serenity".

Silverhold is eight sectors away from St Albans. The Silverhold Colonies are the jurisdiction of Federal Agent Womack in the episode "The Message".

St. Albans is an icy world, and Tracey's home planet. Located about two days away from the Space Bazaar Sky Plex. A Federal station is located nearby. Tracey is brought back to this planet in the episode "The Message".

Three Hills is mentioned by Mal as a location for him to sell his stolen goods at in the episode "Serenity".

Triumph is a primitive and poor border planet, apparently self-governed with rather unusual customs and traditions. Elder Gomman is the leader of the planet's settlers. Saffron was picked up here in the episode "Our Mrs. Reynolds".

Verbena was formerly a poor and undeveloped frontier planet, the Alliance chose it as a site of a new gearshift assembly factory for military skiffs. Appears in the unaired script "Dead or Alive".

Whitefall is fourth moon of Athens, a large percentage of which is owned by a woman named Patience. Whitefall is said to not be civilization "in the strictest sense". The crew visits Whitefall hoping to sell their cargo to Patience in the pilot episode.