Mithrim was a region of Hithlum inhabited by grey-elves. It was surrounded by mountain ranges on three sides, with Lake Mithrim at its core.

When hosts sons of Fëanor arrived back in Middle-earth in their pursuit of Morgoth, their camped at the lake. With the rising of the Sun, the hosts of Fingolfin also arrived in Mithrim.

Fingolfin and Fingon ruled Mithrim but eventually, after Nirnaeth Arnoediad, The Battle of Unnumbered Tears, Mithrim was overrun and occupied by swarthy men, loyal to Morgoth.