The Dwarves of the Iron Hills belonged to the house of the Longbeards, otherwise known as Durin's Folk. Originally, the Dwarves of this house dwelt in the northern Grey Mountains, but they were greatly troubled by Dragons in that region. After King Dáin I was slain by one of these dragons, his surviving sons led an exodus into the east. Dáin's elder son Thrór recreated the Kingdom under the Mountain at Erebor, while his younger brother Grór led a part of the people further into the east, to settle among the Iron Hills.
The Dwarves of the Iron Hills is known to have been joined by the Ironfist clan led by Krínan Ironbeard, whom descended form both Ironfists and Ironbeards. The Ironfists was amongst the minor clans such as Ironbeards and Stiffbeards, which is the main reason for combining and reinforcing with the dwarves of the Iron Hills. This happened during the late Third Age.