The Outer Colonies are the human-colonized planets farthest from the Inner colonies such as Earth and Reach, with colonies founded after. Until the Human-Covenant war, disorder and rebellion were commonplace. By 2531, the majority of the Outer Colonies had been glassed by the Covenant.
Beginning in 2525, Harvest was the first world to fall to the Covenant's genocidal wrath. In 2535, after ten years of war, most of the Outer Colonies had been lost, with Jericho VII being among the last major ones to fall. By 2552, though some Outer Colonies still remained in UNSC hands (mostly remote outposts), most were small and rather insignificant worlds. The few significant colonies still under UNSC control lived in constant fear of Covenant invasion. Some of the remaining colonies were bases for outlaws. By the time the Human-Covenant war ended on March 3, 2553, tensions in the remaining worlds had presumably died down significantly, however some colonies refused to negotiate with the UNSC and Venezia did not allow a UNSC ship to land, thus leading to the UNSC ships destruction, which then Captain Osman vowed to avenge.
- Eridanus II - Planet glassed by the Covenant in 2530
- Eridanus Secundus - Asteroid with a rebel base, presumably destroyed by the Covenant in 2552
- Victoria - Planet with unknown status
- Arcadia - Planet attacked unsuccessfully by the Covenant in 2531, but attacked again and destroyed in 2549
- Madrigal - Planet glassed by the Covenant in 2528
- The Rubble - Abandoned and destroyed except for Habitat Exodus
- Roost - Planet with unknown status
XI Boötis A System - System still held by UNSC
Beta Centauri - System with unknown status
Dwarka - Planet presumed glassed by the Covenant, as all contact was lost
Paradise Falls - Planet with unknown status
Sansar - Planet glassed by the Covenant, date unknown.