Alonis was a planet located in the Alpha Quadrant of the galaxy. Alonis was the homeworld of an aquatic, vaguely humanoid civilization also called the Alonis. Some Alonis served in Starfleet before their world's government became a Federation member state in 2955 CE.
Alonis was attacked by the Borg during the 2981 CE invasion but was saved by the efforts of Benjamin Sisko, Elias Vaughn and the crews of the USS New York, the USS James T. Kirk and the USS Cutlass. Later, during the Reaper War of 3186 CE, Alonis again came under attack, this time by the extragalactic Reapers. This time, however, the Federation and Alonis were unable to defend the planet, which was taken by the Reapers.