Cardolan stretched from the river Baranduin (Brandywine) to the Mitheithel (Hoarwell). Its northern border was the Great East Road, but Cardolan also claimed the Weather Hills, which contained the fortress of Amon Sûl (Weathertop). Amon Sûl housed a palantír, and for this reason it was also claimed by Rhudaur. This lead to a bitter conflict which continued until Rhudaur became a vassal of Angmar after the line of the Dúnedain failed there.
When the kingdom of Angmar appeared in northern Eriador, Cardolan became the most important ally of Arthedain. It had to fight the combined armies of both Angmar and Rhudaur. It soon became apparent that Cardolan could not hold back the forces of Angmar, and in its last years the people became entrenched in their capital region, Tyrn Gorthad (the Barrow-downs). This position became unholdable after Angmar sent evil spirits to inhabit the downs (the barrow-wights). Arthedain could provide little aid, as it was itself under attack. Around T.A. 1409 Cardolan was destroyed, and its former inhabitants accepted the King of Arthedain as their lord. Arthedain managed to reconquer the land briefly, but few people wished to live there on account of the Barrow-wights, and Cardolan was soon lost again.
After the final fall of Arnor, and the destruction of Angmar at the Battle of Fornost, Cardolan remained an unpopulated area until the reestablishment of the northern kingdom under king Elessar at the end of the Third Age.
The name Cardolan appears to be dialect Sindarin for "Red Hill Land".