] ...There was a Mr Darcy in Derbyshire, of some note in 1688. Could he be the source?

The Earls of Holderness are descended from the Fairfaxes and the Middletons. Also related to Diana Willoughby (through Elizabeth Cecil) who is reputed to perhaps be a candidate for Aphra Benn's mother so a good genetic heritage of Names JA Used plus Connection with Female Writer.

These Darcys are tangentially related to JA's own and are also related to the Cravens/Thomas Fowles (to whom Cassandra Austen was engaged)