Dwarves of the Grey Mountains
The Earliest Settlements
The Dwarves of Durin's folk considered the Ered Mithrin as part of their land as far back as the reign of Durin I. Because of constant attack by both Orcs of Morgoth and possibly Dragons, they were not heavily explored or settled until the Third Age.
The Awakening of Durin's Bane
Durin's folk started to gather in the Grey Mountains in T.A. 1981 after a Balrog was awakened in their ancestral home of Khazad-dûm, which its people fled in fear. Another portion of Durin's folk lead by King Thráin I established the Kingdom under the Mountain at Erebor. Some years after leaving Moria Scatha, the Great Worm of the Ered Mithrin began to afflict the Dwarves and all who lived in that region, until Fram of the Éothéod slew him, bringing peace from the Long-Worms from many years till the Wars of the Dwarves and Dragons. But there was a feud between the Dwarves and Fram, for he refused to yield any of the treasure of Scatha to the Dwarves. Instead he sent a necklace of Scatha's teeth to them, saying "treasures like these are hard to come by". For this insult it is said the Dwarves slew him.
The Seat of Durin's Realm
In T.A. 2210 King Thorin I, learning that most of his people were gathering in the Grey Mountains, left the Lonely Mountain to join the Dwarves to the north, for those mountains were rich and little explored.
The War of the Dwarves and Dragons
For many years Durin's folk prospered in the Ered Mithrin, but the Dragons in the wastes beyond began to multiply again and made war on the Dwarves in T.A. 2570, and plundered their works. After 19 years the War of the Dwarves and Dragons came to an end when a great Cold-drake killed King Dáin I, and his second son Frór at the door of his hall. A year later most of Durin's folk abandoned the Grey Mountains. Grór, youngest son of the king went with many followers to the Iron Hills. In the mean time, the new King Thrór along with his uncle Borin, and the remainder of the people went back to Erebor.
Remaining Peoples, and Later History
There still was a remnant of the Dwarves in the Ered Mithrin after the core of the population left, but were probably few. Working whatever mines they could hold from the Orcs and Dragons, but is speculated that they may have left at some point as well. It is likely that the Dwarves reclaimed all their old halls and mines sometime during the Fourth Age, if not after Dáin II Ironfoot became king of Durin's folk in the late Third Age.