It seems that my mother's family, Kollenborn, came from Romanshorn, Switzerland, near the German border and the Bodensee/Lake Constance (Konstanz).
I have found Kollenborn to be an extremely rare name - none in the Munich or Berlin phonebooks when I looked, but there were quite a few in the Romanshorn book when I looked (1980, when I was passing through). I did not look in any phone books of Swiss cities such as Bern, Basel, etc.
Does anybody know of any other location where Kollenborns lived, or anything else about them? Danke im voraus.