Colonies in the Reunited Kingdom:
There are two colonies of which Tolkien notes in the lands of the Reunited Kingdom, one of these falls in Gondor and the other In Rohan. The first I shall talk about is the one in the lands of Gondor, more specifically the lands of Ithilien. This is presumably the smaller of the two colonies and is lead by Legolas of the Woodland Realm, Tolkien notes around the year 20 of the Fourth Age Legolas leads elves out of the Greenwood and they dwelt in the lands of Ithilien for that of at least 100 years. As these elves reside in the lands of Ithilien they would fall under the King of the West though the whole of Greenwood would not fall under the rule. I mark this kingdom with a small dot in Ithilien as their exact position in these lands is not stated, and under Faramir they are still owned by Gondor. The second of the two colonies in the lands of the Reunited Kingdom falls in the vassal Kingdom of Rohan, it is the colony established by Gimli in the Glittering Caves behind Helms Deep in the beginning of the Fourth age. I note them here as a colony and not under the realm of Durin as though they are dwarves of Durin's Folk, Tolkien makes no mention of Rohan giving the caves nor the Hornburg to the Dwarves and therefore the lands would still be that of Rohan and the Dwarves under them much like the Elves of Ithilien.