William Mostyn

William Mostyn (June 5, 1836– March 30, 1881) was an Irish-born doctor and political figure in Ontario. He represented Lanark North in the Legislative Assembly of Ontario from 1875 to 1879 as a Conservative member. He drowned at the age of 44.

Of Welsh descent, he was born in Elphin, County Roscommon and came to Upper Canada with his parents in 1837. Mostyn was educated in Kingston and received his M.D. from Queen's University in 1858. He served as a surgeon for the militia. Mostyn was president of the North Lanark Agricultural Society. He served three years as reeve of Almonte and 15 years as assistant coroner for Lanark Ontario. Mostyn was also a district Grand Master in the Freemasons.