I’ve know for some time that the Kilpatricks were kin, their name being a variation of Kirkpatrick. Tonight I stumbled upon an interesting explanation for the difference. The source is an old Kirkpatrick Newsletter dated Oct-Nov-Dec 1989. It was published by Nathan L. Barlow of Rison, Arizona, whom I have not been able to locate online. If anyone knows of him, please contact me!
Anyway, the article was written by George M. Kirkpatrick of North Syracuse, NY.
While there were many with the surname Kirkpatrick in America prior to 1800, it is difficult to find documentation to establish family lines. A further difficulty is found in the use of various surname spellings, particularly prior to 1800. Kirkpatrick and Kilpatrick are used almost interchangeably (and also Killpatrick). It seems likely that Kilpatrick is closer to the original surname spelling and that Kirkpatrick is the anglicized version… The Kilpatrick spelling is still found near Glasgow, Scotland as in the towns of ‘Old Kilpatrick’ and ‘New Kilpatrick’ while the Kirkpatrick spelling is common near the English border, e.g. near Closeburn and Dumfries. All three versions are still in use, however.