William Barber (1819-1889) was a Canadian businessman and member of the Legislative Assembly of Ontario for Halton from 1867 to 1875.

His family came to Canada from County Antrim in Ulster, Ireland in 1822. The four Barber brothers built a woollen mill, foundry and sawmill in Georgetown, Ontario. In 1854, they built a paper mill on the Credit River near Streetsville, Ontario. In 1888, his nephew, John Roaf Barber, upgraded the mill to use hydroelectricity power, one of the early industrial applications of electricity in Canada.

In 1862, Barber built a brick home near Streetsville, Ontario now known as The Old Barber House.