This region was in the far east of Middle-earth southeast of Cuiviénen and the Orocarni (the Red Mountains), the awakening place of the elves. Throughout the ages, Hildórien faced the East Sea and continued to do so ever after.
According to legends of the Edain, Morgoth visited Men in Hildórien and converted them away from Eru Ilúvatar, and Men were made mortal in divine punishment. However, this was merely a trait bestowed upon men by Eru and not out of punishment. To escape the evil of Morgoth and his followers, the Atanatári were the first to flee Hildórien, travelling west to eventually Beleriand. However, the men that continued to worship Morgoth followed later on in the First Age with the promise that if they served him, they would receive the rich lands of the Beleriand as payment.
Hildórien was possibly deserted by the race of Men and no longer inhabited by the time of the War of the Ring, when Middle-earth had gotten a new terrestrial landscape at the beginning of the Second Age.
Hildórien is a Quenyan word for 'Land of the Followers'.
- The Atlas of Middle-earth pgs. 5 & 39