To the west and south it had a long shore with the Great Sea Belegaer, to the north were the highland regions of Hithlum, Dorthonion and the hills of Himring, to the east the Ered Luin (Blue Mountains) reached nearly to the sea. The land of Nevrast in the northwest was sometimes considered part of Beleriand.
The River Sirion, the chief river of Beleriand, running north to south, divided it into West Beleriand and East Beleriand. Crossing it east to west was a series of hills and a sudden drop in elevation known as Andram, the Long Wall. (The river sank into the ground at the Fens of Sirion, and reemerged below the Andram at the Gates of Sirion.) To the east of the Long Wall, was the River Gelion and its six tributaries draining the Ered Luin, in an area known as Ossiriand or the Land of Seven Rivers. The River Brethin and the River Nenning were the two lesser rivers of the western land of Falas.
In addition, fulfilling a prophecy, the graves of Turin Turambar and Morwen survived as the island Tol Morwen. Likewise part of Dorthonion became Tol Fuin, and the Hill of Himring became the island of Himling. All of these together were known as the Western Isles.
A map of Beleriand, courtesy of the Encyclopedia of Arda