Heidegger's Bible Handbook: 1 John: Recipients, Part 2
3. The assertion of Baronius and Grotius, that it was formerly inscribed to Parthians, is touched upon.
Therefore, Baronius is deceived, who on the year 99 AD insists that this Epistle was written to the Parthians, relying on the testimonies of Hyginus,Epistle I, and of Augustine in Quæstionibus Novi Testamenti, question 39. With whom Grotius agrees, by Parthians understanding Jews converted to Christ that were living, not under the empire of the Romans, but of the Parthians, in locations on the other side of Euphrates, where was a great multitude of Jews, as at Nehardea, Nisbis, etc. Which things are altogether inane, neither are they confirmed by the authority of Hyginus or Augustine. For, the writings to which Baronius appeals are Pseudepigraphical and spurious. Those Epistles of the Roman Pontiffs, among which is that ascribed to Hyginus, and which are enumerated in the tomes of the Councils, in the absurdity of style and matter differ much from the writers of that age. Also, the Quæstiones Novi Testamenti, passed off under the name of Saint Augustine, do not even belong to a Catholic writer, much less to Saint Augustine, indeed, with even Bellarmine himself in Tome III de gratia humano, chapter I, as judge. Whether Saint John preached the Gospel to the Parthians, is uncertain. While the ancients make Thomas the Apostle of the Parthians. Nevertheless, if he preached to them, why he would intend the Epistle to them, rather than to the Ephesians, among whom he lived long and is buried, no reason is able to be given.
 Hyginus was bishop of Rome from about 138 to 142.  Nehardea was located in what is now central Iraq.  Nisbis was located on what is now the south-eastern border of Turkey.