split off from I in the sixteenth century.
J
the youngest letter of the alphabet. The Italian Gian Giorgio Trissino argued in 1524 that I was doing two jobs, and English took another century to agree. Shakespeare's first editions print I where we write J: Iulius, Iohn.
Jackson · James · Jansen · Jenkins · Jimenez · Johnson · Jones · Jordan · Meijer
In the modern alphabet this letter is number 10 of 26. Before it comes I, after it K. The order itself is inherited: Latin took it from Greek, Greek from Phoenician, and the sequence has survived largely unchanged for about three thousand years. Every rearrangement since has been an insertion, not a reshuffle.
This is a consonant: it sets the hardness of a name and how it meets the next word. In a corpus of 315 surnames this letter opens 8 and closes 0. Among the 96 given names in the base it appears in 9. One occurrence per surname is the ceiling: no surname in the corpus repeats this letter.
James · John · Joseph · Jacob · Benjamin · Jack · Jennifer · Jessica · Julia
Nobody inherited these letters: they were made, because the sound they carry had no Greek sign.