The Old Forest is a small forested area which lies east of the Shire. It is one of the few survivors of the primordial forests which covered most of Eriador before the Second Age, and it once was but the northern edge of one immense forest which reached all the way to Fangorn Forest.
It is bordered in the east by the Barrow-downs, and in the west by The Hay, a large wall which the Hobbits of Buckland built after they cut the forest to make room for their new homes. When the trees grew too close to the hedge, hobbits cut down the trees nearest and created a clearing by a bonfire. Ever since then, the trees were more hostile.
The Hobbits believed the trees of the Old Forest were in some manner 'awake', and were hostile. They swayed when there is no wind, whispered at night, and misled travellers deeper into the forest. This was a Hobbit legend well-based on fact. The trees carried a malice and a hatred, though not connected to the evil stemming from the East and Mordor; the hobbits mostly referred to the forest as queer and dangerous rather than evil.
No doubt angered by the years tree-felling and destruction that they had witnessed, the trees would indeed lash out at travellers, whether they meant good or ill. Frodo, Merry, Pippin and Sam were waylaid by a falling branch as they passed through, and the hobbits had the sense that they were being watched angrily by the trees, and forest itself. The paths in the forest, which seemed at first to be true, would angle downward into the valley of the Withywindle. The forest seemed bent on forcing all travellers in that direction.
It is probable that some trees of the Old Forest were Huorns.