The Kingdom of Breifne or Bréifne (; anglicized Breffny, Brefnie, Brenny) was the traditional territory for an early Irish tribal group known as the Uí Briúin Bréifne. The Bréifne territory included current day Irish counties of Leitrim and Cavan, along with parts of County Sligo (an area roughly equivalent to the modern Roman Catholic Diocese of Kilmore).