There was an old family story told that the Dawson family was not originally English, but that John Hughes Dawson’s family came to Cornwall from Ireland. There was a family legend that they were descended from an Earl of Portarlington. Portarlington is just west of Dublin, in country Laois, in modern Eire.
The Earl of Portarlington was indeed a John Dawson, who was already the 2nd Viscount Carlow. The title was created in 1785 for him. He had previously represented Portarlington in the Irish House of Commons.
He was the son of William Dawson, who had represented Portarlington and Queen’s County in the Irish House of Commons, and had been created Baron Dawson, of Dawson’s Court in the Queen’s County, in 1770, and Viscount Carlow, in the County of Carlow, in 1776.
All of this information I found in Wikipedia.
Our John Dawson was born in Kent to Richard Dawson, who was also born in Kent, as were the Dawsons for generations before as this family history shows. The first Dawson of this family to come to Kent came from Cumberland, in the 16th century. They seem to have come from a long line of English peasant farmers and agricultural labourers. So it doesn’t appear at all that there is any truth to this claim to aristocracy.
The only tiny possible hint is the birth of Richard Dawson (IV), illegitimate son of Richard Dawson (III) and Elizabeth Forbister, in 1763. But children born out of wedlock is a very common occurrence throughout history.
I suspect the story was told by a butler (John Hughes Dawson) to his children, who in turn continued it down to their children, especially once they were living in a small isolated pioneering community on the other side of the world.
Croft’s Peerage website
update: 30 June 2019