Williams started as a way to say “William’s child.” William, brought by the Normans, flooded English name lists, so the genitive ending -s (“of William”) stuck as a surname. In Wales the same idea often comes through the older patronymic ap Gwilym—“son of Gwilym,” the Welsh form of William—later smoothed into Williams on English records.
So two related paths land on one spelling: English “William’s” and Welsh “son of Gwilym.” Either way, the name is a parent marker, not a job or a hillside. That shared pattern helps explain why Williams ranks among America’s everyday surnames without needing a single founding couple.