The river Adorn occurs in J. R. R. Tolkien's fictional universe of Middle-earth.

The river Adorn was one of the rivers which arose in the Middle-earth, and together with the river Angren (or Isen) formed the western border of the Kingdom of Rohan. The Adorn joined with the Isen about 150 Númenórean miles west of the Gap of Rohan.

The triangle of land between the Isen, Adorn, and the White Mountains was nominally part of the Kingdom of Rohan, but in the late Third Age it was a contested area between the Rohirrim and the Dunlendings.