Ohio

Finally I have found the origin of 'Ohio' in Schoolcraft; I had always thought it was a Shawnee word meaning 'beautiful', and I was close:

Committing my baggage to a carman, I ascended the bank of diluvial earth
and pebbles with all eagerness, and walked to the point of land where
Fort Pitt (old Fort Du Quesne) had stood. It is near this point that the
Alleghany and Monongahela unite, and give birth to the noble Ohio. It is
something to stand at the head of such a stream. The charm of novelty is
beyond all others. I could realize, in thought, as I stood here, gazing
on the magnificent prospect of mingling waters, and their prominent and
varied shores, the idea, which is said to be embodied in the old Mingo
substantive-exclamation of O-he-o! a term, be it remembered, which the
early French interpreters at once rendered, and truly, it is believed,
by the name of _La Belle Rivière_.