The Mephout Dominion was an isolated Wild Space sector located on the edge of the known galaxy. It contained the Mephout system, which was home to the sentient Mephout species.
In 4 ABY, the Nagai attacked the Mephout Dominion.
The area of space surrounding the Mephout system was explored between 1000 BBY and 25 BBY. Until the Mephout Dominion was discovered by the Galactic Empire, nearly all translating duties in the sector were carried out by the Mephout-designed RST Model Translator Droids. However, due to the droids' high susceptibility to electromagnetic pulses, which tended to interfere with their rationality circuits, the units caused numerous problems during important government functions, leading to the issuance of a marriage proposal and half a dozen declarations of war as well as a dozen assassinations being carried out.
As part of their incursions in the galaxy in 4 ABY, the extragalactic Nagai raiders successfully assaulted the Mephout system as part of an attack on the Mephout Dominion's government, which at that point had not yet officially aligned itself with the Alliance of Free Planets.
The Mephout Dominion was first mentioned in the Star Wars: The Roleplaying Game statistics included with the comic story "Bungo n' Rusti Get Carry-Out," which was authored by Jim Anderson and published in the November 1996 eleventh issue of West End Games' Star Wars Adventure Journal.