Originally an autonomous part of the kingdom of Connacht, it later became one of the vassal territories of the Mac William Íochtar.

Umhaill's last and most famous ruler was Grace O'Malley (Gráinne Ní Mháille), nicknamed "the pirate queen".

In 1576, during the Tudor conquest of Ireland, she agreed to the surrender and regrant policy, accepting English inheritance law in return for official title deeds to her lands.

Knox says of Murrisk "With Burrishoole it forms the kingdom of Aicill and Umall, which comes into history at the battle of Moy Lena.

The Gaelic culture and Irish language continued on in the area longer than most other parts of Ireland.