When William L Mahaney was born on 15 September 1847, in Michigan, United States, his father, David L Mahany, was 32 and his mother, Sarah Ann Murray, was 24. He married Catherine Dickinson on 13 March 1872, in Butler, Branch, Michigan, United States. They were the parents of at least 1 son. He lived in Chicago, Cook, Illinois, United States in 1910 and Homer, Calhoun, Michigan, United States in 1920. He died on 21 May 1924, in Jackson, Jackson, Michigan, United States, at the age of 76, and was buried in Homer, Calhoun, Michigan, United States.