William Tennant Mortlock (1858 – 17 August 1913) was a South Australian grazier and politician.

He read for the law at the Inner Temple while in England, but returned to South Australia in 1883 and did not pursue his legal studies further.

[2][3] In 1891 he purchased Martindale Hall at Mintaro, which would become his family's main station.

He died in a private hospital in North Adelaide in 1913, aged 55, following a six-month illness.

He was interred in the Mortlock family vault at the North Road Cemetery.