Mary Frances Dawson, Countess of Dartrey, 25th Baroness de Ros of Helmsley (née FitzGerald-de Ros) (31 July 1854 – 4 May 1939) was a British peeress. She was born in London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

. Her parents were Dudley FitzGerald-de Ros

Dudley FitzGerald-de Ros, 24th Baron de Ros

Lieutenant-General Dudley Charles FitzGerald-de Ros, 24th Baron de Ros of Helmsley, KP, KCVO was the son of William FitzGerald-de Ros and Lady Georgiana Lennox. He was born in Brighton....

 and Lady Elizabeth Egerton. Upon her father's death in 1907, Mary succeeded to the title.

The 25th Baroness married Anthony Dawson, 3rd Earl of Dartrey

Earl of Dartrey

Earl of Dartrey, of Dartrey in the County of Monaghan, was a title in the Peerage of the United Kingdom. It was created in 1866 for Richard Dawson, 3rd Baron Cremorne. The Dawson family descended from Richard Dawson, a Dublin banker who also represented County Monaghan in the Irish House of Commons...

 (1855-1933) in London on 2 October 1878. To them were born three daughters; the Barony of de Ros descended among their issue:

• Lady Una Mary Dawson
  Una Ross, 26th Baroness de Ros
  Una Mary Ross, 26th Baroness de Ros of Helmsley succeeded her mother to the title in 1943...
  
  (born 1879), who became the 26th Baroness upon the termination of the abeyance in 1943.
• Lady Maude Elizabeth Dawson (born 1882)
• Lady Eleanor Charlotte Augusta Dawson (born 1885)