Hellanicus of Mytilene, born 60 years before Plato, of whose 22 books we sadly only have fragments, wrote about Atlantis around 405 (when Plato was about 20).

Hellanicus of Mytilene, born 60 years before Plato, of whose 22 books we sadly only have fragments, wrote about Atlantis around 405 (when Plato was about 20). For him Atlantis was the daughter of the titan Atlas. A small fragment of Hellanicus’s opus about her survives with the following line: "Poseidon coupled with Celaeno, and their son Lycus was settled by Poseidon in the Isles of the Blessed and made immortal.". "The Isles of the Blessed" would become Atlantis the geographical location in Plato's writing. The fragment was found in the Oxyrhynchus Papyri 11, 1359. Certainly not a lot or a bullseye, but there you go. If you permit me, I'd like to make a suggestion to you : always applying the (IMHO) fallacious rule "apparent absence of evidence is evidence of absence" makes life very drab. Letting oneself dream of utopias past or future improves creativity, and gives hope and a nice escape from the rat race. Don't spoil other people's fun with cynicism.