Fangorn forest was the easternmost remnant of the immense forest that spanned all of Eriador and Calenardhon in the First Age and early Second Age. Treebeard expressed a deep sadness at the loss of the forest primeval to the Orcs and to the age of Men and their machines. The rest of the forest was destroyed by the Númenóreans and Sauron. It was the oldest part of Treebeard’s realm, and the Ents’ last retreat.

The Forest of Fangorn was located at the south-eastern end of the Misty Mountains near the Gap of Rohan. The mountains formed the western border of Fangorn. At the end of the mountain range stood the stronghold of Isengard near the southwestern corner of the forest and this was where Saruman lived.[citation needed] To the east and south of Fangorn was the land of Rohan, and Lothlórien lay to the north and slightly east. Fangorn Forest stretched for many miles and held many paths.

Tolkien stated that two significant rivers ran through the forest. To the north the Limlight flowed from the woods and then formed the northern border of Rohan. The river then merged into the larger Anduin. In the south, the Entwash spread deep into the forest arriving from Methedras, a mountainous region located near the Misty Mountains. The river then flowed from Fangorn and was directed through Rohan to the Anduin River. The valley of Derndingle was located to the south-west. There was a path where the Entwash passed into a region called Wellinghall and this was where the Entwash passed the home of Treebeard, the shepherd of the forest.

Fangorn Forest was said to be humid, and trunks and branches grew thick where very little light penetrated the forest. Similarly, Fangorn was said to be a dangerous and evil place like Mirkwood where huge spiders roamed the forest and other evil creatures lay, but this was not the case following the events of Lord of the Rings. The forest was home to many different kinds of trees. Huorns also lived in the forest, similar to Ents but more discreet. Most lived deep in the Forest of Fangorn. The Ents and Huorns drank from the river Entwash, and from it the Ents brewed their legendary drink, the Ent-Draughts.