From Halopedia, the Halo wiki
As a Tier 2 species, the Sangheili colonized and surveyed a range of planets in the centuries before and after the formation of the Covenant. Developed worlds are governed by hundreds of clans and their keeps, each competing for power and influence using both politics and military force. Smaller colonies are often governed by only a handful of keeps, which control the entirety of the world's resources.
After achieving space flight, the Sangheili began traveling from Sanghelios to colonize other worlds. Qikost and Suban, the moons of Sanghelios, were among the first colonized, with the Sangheili setting up armories on Qikost and mines on Suban. Other worlds were soon colonized. The Sangheili spread to the stars searching for both resources that could be used to build and power spaceships, and planets which contained Forerunner relics to worship. By the time of the San'Shyuum-Sangheili War, there were a total of seventy-six Sangheili colonies. It was on one such world, Ulgethon, that the Sangheili first encountered the San'Shyuum.
Following the end of the war and the formation of the Covenant, Sangheili colonies became anchor points for Covenant. While High Charity was the political center of the alliance, Sanghelios and its colonies became the place where warriors would be recruited for the Covenant military. After Sanghelios, the important worlds were Sangheili fortress worlds, examples of which include Saepon'kal and Malurok.
Following the end of the Human-Covenant War, the Sangheili, lacking a centralized government, were thrown into political turmoil, ultimately resulting in civil war. While some colonies, like Hesduros, would join the Covenant remnants, most colonies like Duraan, Khael'mothka and Rahnelo joined with Sanghelios under Arbiter Thel 'Vadam's new Swords of Sanghelios, fighting off the other remnant groups and the Jiralhanae. The Office of Naval Intelligence found it difficult to track the true extent of the Sangheili colonial sphere and the military growth present in the dozens of active Sangheili colonial polities, particularly due to their differing political structures.
Just days after a tentative peace treaty was formed between the group that would become the Swords of Sanghelios and the UEG, the Sangheili colony of Glyke was mysteriously destroyed, killing billions. Rumors had it that the colony's destruction was either an internal conflict or a Jiralhanae retaliation, but in truth it was destroyed by SPARTAN-II Gray Team with a NOVA bomb as part of Operation: SUNSPEAR, an effort to strike a blow at a major enemy world to try to cause the Covenant to reconsider. Having last heard that Earth was under attack, Gray Team were unaware of the war's end due to damaged deep-space communications equipment and thus that their mission was no longer necessary. When Gray Team resurfaced in 2558, Thel 'Vadam agreed to pardon the three Spartans for the action instead of trying them as war criminals for genocide as part of a deal ONI offered to have Gray Team join an interspecies strike force operating in the Joint Occupation Zones.
List of known colonies