This supposed claim of a Knox link to William the Conqueror, may have come from a misunderstanding.
I was about to post a piece from the 1824 document last night which appears to link Rev Knox of the Parish of St Catherine, in the City of Dublin, to a Knox at a place called Strokestown, County Roscommon.
Interesting to note a reference to Strokestown in the published "Knox of Prehen".
I attach Knox of Prehen.
In a Marriage Settlement document there was a reference to Faren[?] Cottage, probably the one spelt Farn in the attached history.
See Knox's Marriage Settlement 1824, Registered 20th January. Also the full document at Reply 79 (only parts attached).
Don't be disappointed, the initial glances of the documents available, suggest this family of yours appear to have an interesting history.
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Yes, most people have got to get a documented History back to a 'Gateway Ancestor' who appears in one of the long Rolls they roll out at The College of Arms (if in England), or the Court of Lord Lyon (Scotland), or the country's equivalent.
Mark
Added: Knox of Kilmannock