Una Mary Ross, 26th Baroness de Ros of Helmsley (born Lady Una Mary Dawson) (5 October 1879 – 9 October 1956) succeeded her mother to the title in 1943. She was the daughter of Anthony Lucius Dawson, 3rd Earl of Dartrey and Mary Dawson

Mary Dawson, Countess of Dartrey

Mary Frances Dawson, Countess of Dartrey, 25th Baroness de Ros of Helmsley was a British peeress. She was born in London. Her parents were Dudley FitzGerald-de Ros and Lady Elizabeth Egerton...

, who held the barony in her own right.

The 26th Baroness married Arthur John Ross (died 1917) on 30 July 1904, and they had at least two children:

• Lieutenant Commander The Hon. Peter Ross, RN
  Royal Navy
  The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...
  
   (8 August 1906 – 1940), married on 10 September 1929 to The Hon. Angela Dixon, from whom descends the current holders of the title:
  • Georgiana Maxwell, 27th Baroness de Ros
    Georgiana Maxwell, 27th Baroness de Ros
    Georgiana Angela Maxwell, 27th Baroness de Ros of Helmsley succeeded her grandmother Una Ross after the title was called out of abeyance in her favour in 1958. She was the first woman of her line to be allowed to sit in the House of Lords after the Peerage Act 1963.The 27th Baroness was the...
    
     (1933-1983)
  • Hon. Rosemary Ross (born 14 January 1937), married in 1973 to Beresford Osborne, and had:
    • Joanna Elizabeth Osborne (born 1975), unmarried and without issue
• The Hon. Charles Dudley Anthony Ross (5 October 1907 - 1976), married firstly on 31 August 1940 to Lady Elizabeth Jocelyn (died 1982) and secondly in 1953 to Mary Margaret Graham (died 1994), without issue, and had by first wife:
  • Anthony Arthur Ross (born 27 July 1941), married in 1969 to Joan Cahn, and had:
    • Zara Gail Ross (born 1971), married in 1994 to Stephen Mark Sanders, without issue
    • Deborah Kim Ross (born 1972), unmarried and without issue