Algernon Henry Mills, son of the 1st Baron Hillingdon) and his younger brother was Hon.

Montagu Francis Beauchamp Seymour Dawson-Damer (who married Margaret Stirling Macleod).

[1] Upon inheriting the earldom, Portarlington also inherited Emo Court, a large neo-classical mansion near the village of Emo in County Laois, Ireland designed by the architect James Gandon in 1790 for John Dawson, 1st Earl of Portarlington.

Together, they were the parents of:[1] Lord Portarlington died of "congestion of the kidneys" at the Royal Palace Hotel at Ostend, on 31 August 1900 at age 42.

[1] Through his daughter Lady Christian, he was a grandfather of Rosemary Lusia Bowes-Lyon (1915–1989), a first cousin of Queen Elizabeth II who married Edward Wilfred George Joicey-Cecil, youngest son of Col. Lord John Joicey-Cecil, MP for Stamford (a son of the 3rd Marquess of Exeter), in 1945.