William Henry Allen was born in Lenton, Nottingham, Nottinghamshire, England in early 1873. He was later baptised in Coventry, Warwickshire on 30 July 1876. He was the son of Alfred Allen (b. 1849), a turner and later a factory foreman, and Hannah Selina Hunt (b. 1851), natives of Birmingham who were married in early 1872, and William was one of their six children. His siblings were: George Alfred (b. 1874), Arthur Archibald (b. 1876), Florence Louise (b. 1878), Gertrude Miriam (b. 1887) and Elsie (b. 1893).