From A Wiki of Ice and Fire
King's Mountain is a place in the Seven Kingdoms; its location has not been revealed.
A Dance with Dragons
Ser Patrek, one of the queen's men in service to Stannis Baratheon, is a knight from King's Mountain. Patrek loses his lands in southern Westeros when he accompanies Stannis north to the Wall.
Behind the Scenes
Patrek of King's Mountain is named after a friend of George R. R. Martin, Patrick St. Denis of Montreal. The name of Montreal derives from "Mont Réal" or "Mont Royal" in modern French and can be translated as "King's Mountain".