According to Greek mythology, Ion was the illegitimate child of Creüsa, daughter of Erechtheus and wife of Xuthus. Creusa conceived Ion with Apollo then she abandoned the child. Apollo asked Hermes to take Ion from his cradle. Ion was saved (and raised) by a priestess of the Delphic Oracle. Later, Xuthus was informed by the oracle that the first person he met when leaving the oracle would be his son, and this person was Ion. He interpreted it to mean that he had fathered Ion, when, in fact, Apollo was giving him Ion as an adoptive son. Creusa was planning on killing Ion due to her jealousy that Xuthus had a son, and she was still childless. At the same time, Ion was planning on doing harm to Creusa. In the end, Creusa found out that Ion was her child, and only Xuthus' adopted child. His story is told in the tragedy Ion by Euripides.

Ion founded a primary tribe of Greece, the Ionians. He is linked to the Hebrew Javan.