The Boyne River main stream is 5.6 river miles long from its mouth at Lake Charlevoix to the junction of the North Branch and the South Branch just north of Boyne Falls.

The Boyne River North Branch is 5.9 river miles long from the junction of the North Branch and the South Branch just north of Boyne Falls to its source just west of Thumb Lake.

The Boyne River South Branch is 10.5 river miles long from the junction of the North Branch and the South Branch just north of Boyne Falls to its source just south of Elmira.