William Mack (February 29, 1828 – December 11, 1897) was an Ontario businessman and political figure.
He was born in Lanarkshire, Scotland in 1828, the son of Robert Mack, and was brought to Huntingdon County, Lower Canada, by his parents during his first year of life.
Mack went into business on his own, also helping to establish paper, cotton and woollen mills at Cornwall.
He served as reeve of Cornwall in 1871 and 1876 and as warden for the United Counties of Stormont, Dundas and Glengarry in 1878.
His daughter Margaret married Alexander McCracken, who was a mayor of Cornwall, and his son William R. later served as sheriff for the United Counties.