John Leslie born in 1857 the only son of Sir John Leslie, 1st Baronet, and Lady Constance Wilhelmina Frances Dawson-Damer. His father was the Conservative Member of Parliament for Monaghan from 1871 to 1880 and was created a baronet in 1876, and his mother was the daughter of Colonel George Lionel Dawson-Damer.
On 2 October 1884 in New York City, with disapproval from both families, Leslie married Leonie Blanche Jerome, daughter of Leonard Jerome and Clarissa Hall. Leonie's sister was Jennie, wife of Lord Randolph Churchill and mother of Winston Churchill. Leslie and his wife had five children:
Leonie Clarissa Leslie (1884–1945), married with the count Gregório de Almeida
Sir John Randolph Leslie, 3rd Baronet (1885–1971), generally known as Shane Leslie
Captain Norman Jerome Beauchamp Leslie (1886–1914)
Seymour William Leslie (1889–1979)
Lionel Alistair David Leslie (1900–1987)
New York, New York Marriage Index record:
John Leslie and Leonie B. Jerome were married 1 Oct 1844 in Manhattan, New York, USA 
1891 England Census; 53 Seyonsur (?) Street, St. Marylebone, London, England.
John Leslie, 33, head, Cap 5th Batt Royal Fusiliers, b. Kensington, London, England
Leonie B. Leslie, 30, wife, b. St. Germans, France
John R. Leslie, 5, son, b. London, England
Norman P. Leslie, 4, son, b. London, England
William S. Leslie, 1, son, b. London, England
others listed as servants/help not included here. 
1911 Ireland Census, 2 Apr 1911, Glaslough, County Monaghan, Ireland.
John Leslie, head, 53, London, Colonel retired, married
Shane Leslie, son, 25, London, Literature BA, single
Seymour William Leslie, son, 21, London, Electrical Engineer, single
From FindAGrave memorial. No photos of grave. Data, excluding burial location, is unsourced and information only.
COL John “Jack” Leslie was born 7 Aug 1857 and died 25 Jan 1944 (aged 86) in Glaslough, County Monaghan, Ireland. He is buried at Saint Salvator's Churchyard, Glaslough, County Monaghan, Ireland.
Commissioned a 2nd Lieutenant in the Grenadier Guards. Veteran of the Anglo-Egyptian War of 1882. In 1883, he married Leonie Blanche Jerome of New York. In 1902, he saw active service during the Boer War and became a Lieutenant Colonel and the commanding officer of the 12th (Reserve) Battalion, Royal Inniskilling Fusiliers. Served as High Sheriff of County Monaghan in 1905. Appointed Honorary Colonel of the 5th Battalion, Royal Irish Fusiliers. In 1916, he succeeded to the baronetcy (Leslie of Glaslough) that had been granted to his father. Invested a Commander of the Order of the British Empire (CBE) in 1919. Served as the last Lord Lieutenant of County Monaghan, from 1921 to 1922, prior to the establishment of the Irish Free State.
Find A Grave, database and images (https://www.findagrave.com : accessed 22 May 2019), memorial page for COL John “Jack” Leslie (7 Aug 1857–25 Jan 1944), Find A Grave: Memorial #165234338, citing Saint Salvator's Churchyard, Glaslough, County Monaghan, Ireland ; Maintained by Researcher (contributor 48705606).