Blackrock ... Seafield ... Bantry
Devotees of P G Wodehouse are of course well aware that (in those halcyon days) members of the aristocracy would address one another by their estate names. Thus in a chance encounter at the Turkish Baths, the Earl of Dukinfield would peer through the steam and exclaim "What ho, Bootle!", to which the short-sighted Marquess of Bootle would riposte "I say, is that you, Dukinfield?".
And it would be more than likely that each of them owned a largeish estate in the places to which their titles referred. So the genitive "of" implied ownership.
But in the early Middle ages, when surnames were beginning to emerge for commoners (and even patricians), one fertile source would be the place where they were born, or at least lived, or had come from, or whatever the association might be. So in my days at school in Derbyshire, there was a boy by the name of Garstang, and another by the name of Whalley, both place-names in neighbouring Lancashire. And they would have had, some six centuries previously, ancestors named (for example) Anthony of Garstang or William of Whalley, whose offspring retained that toponymic even when moving on elsewhere. And, of course, the genitive gradually disappeared, as there was absolutely no implied reference to ownership or even continued personal association.
Well all this is pretty common knowledge, and you're probably getting impatient.
But the point is that in family trees and genealogy generally it seems to be quite common practice to add a genitive place-name to indicate, or emphasise, where someone had flourished – in addition to their surname. And the possibility does arise that this gets misinterpreted to mean that they owned a large estate, or at least a very imposing residence, in that place.
Let's get down and dirty by mentioning the specific instance of "Richard Hutchins of Blackrock". His surname actually originated mediaevally as 'son of Hugh', though that's of no present relevance. But what did Burke mean by "of Blackrock"?
Blackrock itself is a rather vaguely defined area (principally invoked by estate agents) a few minutes walk down the coast from Bantry. So did Burke mean that Hutchins simply happened to live there, or leased the area from a landowner? In particular, had he built himself a substantial mansion there, which would in all probability be called Blackrock House?
But another reputable source maintains that though there did exist a Blackrock House, it was built over the period 1698-1728 by one Hugh Hutchinson, the brother of Richard's daughter-in-law, Richard himself having (according to Burke) died in 1701.
Other reputable sources tell various different tales, but commonly ascribe the building of Blackrock House to Samuel (rather than Hugh) Hutchinson, who eventually sold it some decades later to Richard White of Bantry (who renamed it Seafield House), forebear of the Earls of Bantry (who renamed it Bantry House).
And there is no suggestion of which I'm aware that Richard Hutchins ever occupied Blackrock House himself.