Eriador

Eriador is a geographic region which includes all the territory north of the River Isen (S. "Sir Angren") and between the Blue Mountains (S. "Ered Luin") and the Misty Mountains. Its imprecise northern border lies along the highland ridge that runs westward from Carn Dûm in Angmar and reaches to the Ice Bay of Forochel. Some accounts place the southern border along the line bounded by the rivers Greyflood (S. "Gwathló") and Swanfleet (S. "Glanduin") Most, however, hold it to be that area north of Gondor's traditional western border.

Source

 * MERP.com Wiki