Number of Elves

[Mhoram]

But now a cry went up, passing up the wind from the south from vale to vale, and Elves and Men lifted their voices in wonder and joy. For unsummoned and unlooked for Turgon had opened the leaguer of Gondolin, and was come with an army ten thousand strong, with bright mail and long swords and spears like a forest. Then when Fingon heard afar the great trumpet of Turgon his brother, the shadow passed and his heart was uplifted, and he shouted aloud: 'Utúlie'n aurë! Aiya Eldalië ar Atanatári, utúlie'n aurë! The day has come! Behold, people of the Eldar and Fathers of Men, the day has come!'

That's the only note on how many were in Gondolin that I can come up with at the moment.