Easton's Bible Overview
The Third Epistle General of John
Is addressed to Caius, or Gaius, but whether to the Christian of that name in Macedonia (Acts 19: 29) or in Corinth (Rom. 16:23) or in Derbe (Acts 20:4) is uncertain. It was written for the purpose of commending to Gaius some Christians who were strangers in the place where he lived, and who had gone thither for the purpose of preaching the gospel (ver. 7).
The Second and Third Epistles were probably written soon after the First, and from Ephesus.
M.G. Easton M.A., D.D., Illustrated Bible Dictionary,
published by Thomas Nelson, 1897. Public Domain.