In April 1931 Cowlishaw's mother and younger sister were killed in a motor vehicle accident. In June 1931 Cowlishaw married Eileen (Bonnie) Wellings Smith of Mosman. His former Newington Headmaster the Rev. Dr Charles Prescott officiated at the service in the Mosman Methodist Church. The Cowlishaw's went on to have four daughters: Elizabeth Madge (Betty) Ewins, Diana Helen Jones, Georgina Louise Robinson and Margaret Ann Windybank. His father died in 1954. Having moved to St Ives, New South Wales, Cowlishaw died in 1983 survived by his wife who died in 1997.
