Dwarves of the Iron Hills

The Dwarves of the Iron Hills belonged to the clan of the Longbeards, otherwise known as Durin's folk. About half a millennium before the War of the Ring, the Dwarves of this clan 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 were prosperous in their new home, and were well known for making a metal mesh that could be used for making flexible items like leg-coverings.

It seems that the two related peoples remained on friendly terms with one another. Years later, when Thrór's descendant Thorin Oakenshield sent to the Iron Hills for aid in restoring Erebor, Grór's grandson Dáin II Ironfoot (named after his illustrious ancestor Dáin I) sent many armoured Dwarves. As events developed, the Dwarves of the Iron Hills proved crucial in winning the ensuing Battle of Five Armies. Thorin died in that battle, and with him the royal line of Thrór. Through his ancestor Grór, the Kingship of Durin's Folk then fell on Dáin. As Dáin II Ironfoot, he removed from the Iron Hills, and re-established a kingdom under the Lonely Mountain.

It is likely that the Dwarves from the Iron Hills, fought in the Northern Campaign during the War of the Ring, but Tolkien never says that they specifically did.