The North American country whose flag features a single maple leaf is Canada.
Canada’s national flag, commonly called the Maple Leaf or l’Unifolié, has two red vertical bands surrounding a white central square. A stylized red, 11-pointed maple leaf appears in the middle. The design was officially adopted on February 15, 1965, a date now observed as National Flag of Canada Day.
The maple leaf had represented Canada long before it appeared on the modern flag. It became a national symbol in the 19th century, appeared on the arms of Ontario and Quebec in 1868, and was added to Canada’s coat of arms in 1921. The flag’s design was created by George F. G. Stanley, with the leaf itself designed by Jacques Saint-Cyr.
A common mix-up is assuming the 11 points have a special symbolic meaning. They do not; the shape was selected partly because wind-tunnel testing showed it remained visually clear in strong wind.