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Probably died 1776.
Burial record for St Andrew, Holborn register dated 8th October 1776 of a Henry Walpole of Gray's Inn Lane.

Page 333 of Watch & Clockmakers of the World lists him as active as a clock and watch maker in 1756 and prior to his entering a mark at Goldsmiths' Hall from near Kings Road, Gray's Inn Lane in 1765.
The Will of Henry Walpole, watch maker late of St Andrews, Holborn, was proved for probate on 7th October 1776 (National Archives reference PROB 11/1024/49).