Isolon III (commonly called Isolon) is a planet within the Gateway Sector. It is the only habitable planet of the Isolon System Isolon III is orbited by two small moons which are currently not inhabitable, but survey teams have identified both as being candidates for localized terraforming within pressurized domes.

The planet itself is Class M with an equatorial diameter of 11,402 kilometers. Isolon has significant dilithium deposits throughout the planetary crust, especially on the northern continent. As a result, mining surveyors and eventually a full-scale colony was established in 2365 to mine and refine the dilithium deposits. The planet has a humanoid population of approximately 350,000. The colony is governed by a democratically-elected council and administrator. The colony provides recruits and supply pipelines for the Gateway Resistance.

The primary Resistance arms supply financier, Dom Riser a.k.a. Merrisod, operated a cache and distribution center on Isolon. The center was destroyed when a segment of the Progenitor, which he had obtained as a possible weapon, overloaded and destroyed the complex from within.