] ...ever come across anything on a Jane, Countess of
> Harrington? I saw a picture of her, painted by Joshua
> Reynolds at the Huntington galleries in California, and was
> very intrigued by her. The picture was painted @ 1777-79
> and she looks to be in her 20s at the time. I did some
> casual glancing through the books I have from that period
> and didn't see her mentioned. Thanks.

According to my 1818 Stockdale peerage, she was Jane Fleming, daughter and co-heiress of Sir John Fleming of Brompton, Middlesex, Bart. She married 22 May 1779 to Charles Stanhope, 3rd Earl of Harrington.

Curiously enough, my 1812 Debrett's does not mention her name. It says:

Charles Stanhope, Earl of Harrington, Viscount Petersham, and Baron Harrington; Commander-in-chief of the forces in Ireland, a General in the army, and a Colonel of the 1st regiment of Life-guards, F.S.A.; b. 20 March 1753; succeeded his father, William, the late earl, 1 April 1779; married 22 May 1779, a daughter and co-heiress (with her sister Seymour, relic of Sir Richard Worsley, Bart.) of Sir John Fleming, Bart. of Brompton-Park, in Middlesex, by whom he has issue, Charles, Viscount Petersham, b. in April 1781. . . .

and it lists seven sons and three daughters. The eldest son, Lord Petersham, was a famed Regency personage-- I think he's the one who was an expert on snuff. One of the daughters married the heir of the Duke of Bedford. All of the sons except the two youngest are officers in the army.

I can't find anything about Jane's father.

Hope that this is the sort of info you were looking for!