Leonard was the youngest son of Herbert Jenner and Elizabeth Summers.
His father was born in Dursley, Gloucestershire, the son of James and Elizabeth Summers and was christened in the parish church on 19 July 1863. His mother was born in Sileby, Leicestershire. Herbert and Elizabeth (nee Marriott) were married in Nottingham in 1888 and had three sons, Arthur Herbert (baptised St Peter Nottingham 10 July 1889), Albert Jenner (b. 1891) and Leonard James (b. 1894). All the children were born in Nottingham.
In 1891 Herbert, a confectioner (bread maker) his wife and first child, Arthur, were living at 5 Mona Cottages, Meadows, Nottingham. Ten years later in 1901 Herbert and Elizabeth, now with three sons, were still living in the Meadows but had moved to 34 Glapton Road. Also in the household was a boarder, George Cottingham (25), who like Herbert was a confectioner (bread maker).
By 1911 the family was living at 55 Holgate Road, Meadows. Arthur (21) and Albert (19) were clerks (railway) and Leonard was a lace warehouseman. There was also a boarder, Daisy Ellis (20), a clerk (chemist), living with the family.
Herbert Summers died in 1912 at the age of 48.
At some point the family moved to 146 Harrington Drive, Lenton, as this was where they were living when his brother Arthur attested on 28 November 1915.
Arthur Summers married Lizzie Bason on 20 November 1915 at St Faith's church, North Wilford. Their daughter, Winifred Ellen, was born the following year on 27 August 1916. a few weeks before Leonard was killed.
At the time of Arthur's death in 1917 his wife and child, mother and surviving brother, Albert, were all living at 146 Harrington Drive. Arthur was a Gunner in the Royal Garrison Artillery and died from wounds received in action on 5 October 1917 (Coxyde Military Cemetery).
Their mother, Elizabeth, died in 1924 age 64. It seems likely that Leonard's niece, Winifred Ellen, married Leonard Cooper in Nottingham in 1946. The third brother, Albert Jenner, married Florence Decima Arthur in Nottingham in 1929. He moved to Doncaster and was living at 24 Crabgate Drive, Skellow, when he died on 29 September 1953.