Gonnus or Gonnos () or Gonni (Γόννοι) was a town and polis (city-state) of the Perrhaebi in ancient Thessaly, which derived its name, according to the later Greek critics, from Gonneus, mentioned in the Iliad. Its position made it one of the most important places in the north of Thessaly. It stood on the northern side of the Peneius, near the entrance of the only two passes by which an enemy can penetrate into Thessaly from the north. The celebrated vale of Tempe begins to narrow at Gonnus; and the pass across Mount Olympus a little to the west of Tempe leads into Thessaly at Gonnus. It was by the latter route that the army of Xerxes I entered Thessaly.