Flag of Ontario
| Use | Civil and state flag |
|---|---|
| Proportion | 1:2 |
| Adopted | April 14, 1965 |
| Design | A red field with the flag of the Royal Union Flag in the canton defaced with the shield of the Ontario coat of arms. |
The flag of Ontario is a defaced Red Ensign, with the Royal Union Flag in the canton and the Ontario shield of arms in the fly. The flag of Ontario was derived from the Canadian Red Ensign that was used as a civil ensign and the flag of Canada from the late 19th century to 1965. When the new Canadian Flag replaced the old in 1965, Ontario changed the Canadian arms on the former national flag to the Ontario arms. May 21 is Ontario Flag Day.