Aerin is a fictional character from J. R. R. Tolkien's Middle-earthlegendarium. She was a woman of the Folk of Hador and related to Húrin Thalion. Her father was one Indor, not otherwise mentioned.

She lived not far from Húrin's house in the south-east of Dor-lómin, but after the defeat of the Eldar and Edain in the Nírnaeth Arnoediad, she was taken to wife against her will by Brodda the Easterling. She secretly helped Húrin's wife Morwen in her poverty, and was beaten by Brodda for it. Yet Aerin managed to keep "some of the kindlier manners of old" in their house, and it became a shelter for homeless and beggars.

When Túrin, son of Húrin, returned to Dor-lómin, he was offered shelter in her house. It was there that he met his old friend Sador Labadal again and learned from Aerin that his mother and sister had gone to Thingol’s realm. Túrin was angered by his cruel fate, and he slew Brodda and additional Easterlings in the rebellion he raised with the servants.

But thereby Aerin’s fate was sealed: her life might have been harsh, yet Túrin's rash act would cause her death through the vengeance of the Easterlings, she explained. He proposed to take her with him and bring her to Doriath but she refused, saying that she would die in the wilds as surely as if she stayed, being old now. Túrin counted Aerin fainthearted and that she was "made for a kinder world"; but Asgon rebuked him: "Many a man of arms misreads patience and quiet. She did much good among us at much cost. Her heart wasn't faint, and patience will break at last." Aerin presumably died in a final act of defiance against the Easterlings, by setting on fire the hall built by Brodda, which Túrin, on fleeing, saw in flames behind him.