This is an extract from a commercial Family Name History company:
"There is a certain amount of confusion regarding the origin of the surname ION (or Ionn or Ions). The most likely explanation is that the name is patronymic in orogon, belonging to that category of names that derived from the forename of a father. In this case, the name simply implies the son/descendent of Ion, very probably a variant of Jon, from John, the meaning of which can be traced to the the old hebrew word which signifies "gracious gift of Yahweh" or "Yahweh has favoured". The earliest recordswould seem to indicate that it was first found in England, as early as the late 13th Century, when, 1273, one Richard Ion of Cambridge was recorded in the hundred rolls.
There is a coat of arms (Though I doubt we're actually entitled to it!) of "Sable, a chevron between three trefoils slipped argent" (Burke's General armory p 543)
Hope this helps.