William Marcus de la Poer Horsley Beresford, 4th Baron Decies DL JP (12 January 1865 – 30 July 1910) was an Anglo-Irish aristocrat.

"[3] At the time of his death he had several horses in training with Pickering at Newmarket and with Major Morris at Wallingford.

[3] On 12 March 1901, Lord Decies was married to Maria Gertrude Willoughby at St Michael's Church in Chester Square (in the Belgravia district of West London).

[4] As Maria's father, Sir John Willoughby, 4th Baronet, had died in 1866, her brother, Maj. Sir John Willoughby, Bt of Jameson Raid fame, gave her away and William's groomsman was his brother, Capt.

"[2] Lord Decies died, suddenly, on 30 July 1910, aged 45, at the Cottage Hospital in Hornsey, after having been "overcome by the oppressive heat" while attending the races at Alexandra Park.