| William Davis Ardagh | |
| Office1: | Ontario MPP |
| Term Start1: | 1871 |
| Term End1: | 1874 |
| Predecessor1: | William Lount |
| Successor1: | Riding abolished |
| Constituency1: | Simcoe North |
| Party: | Conservative |
| Birth Date: | 21 March 1828 |
| Birth Place: | County Tipperary, Ireland |
| Death Place: | Hoboken, New Jersey |
| Occupation: | Lawyer, judge |
William Davis Ardagh (March 21, 1828 - April 16, 1893) was an Ontario lawyer, judge and political figure. He represented Simcoe North in the Legislative Assembly of Ontario from 1871 to 1874.
He was born in County Tipperary in Ireland in 1828 and grew up in County Kilkenny. He came to Barrie in Canada West in 1848, articled in law and was called to the bar in 1855. He entered the practice of law in Toronto with John Willoughby Crawford. He served as deputy judge in Simcoe County in 1882 and was reeve and later mayor of Barrie. He moved to Winnipeg, Manitoba, where he served as Deputy Attorney-General and County Court judge. He also served on the Board of Police Commissioners for Winnipeg.
He died in Hoboken, New Jersey in 1893.