William Lash Miller was born on September 10, 1866, in Galt, Ontario, Canada. William Lash Miller's father was William Nicholas Miller. Lash Miller's uncle Zebulon A. Lash studied law under W. N. Miller at Dundas, and they later practiced law in Toronto together as Beatty, Miller & Lash. Miller and Lash married each other's sisters (Frederica Lash and Elizabeth Miller) in 1864 and 1871 respectively. So William Miller named his first son as Lash Miller, and Zebulon Lash named his first son as Miller Lash.