Andrew McCulloch, again, writing in “Galloway: A Land Apart” writes the following:
“Although the original McCullochs of Myretoun disposed of their family estates in the early 1620s they left numerous descendants, all of whom live in the United States.” According to the author, the McCullochs who remain in Dumfries and Galloway are likely descendents of the McCullochs of Barholm or smaller landowning families, whom McCulloch described as “bonnet” lairds.
We can’t vouch for the statement that all of the McCullochs of Myretoun descendants live in the United States. But the general point that most of the descendants of this line went abroad is certainly noteworthy.