When was the first time the flag flew in a flag day celebration?

The first official Flag Day celebration in the United States took place on June 14, 1877, marking the 100th anniversary of the adoption of the Stars and Stripes as the national flag. However, the concept of honoring the flag predates this event, with various local celebrations occurring as early as the 1860s. Flag Day was later established as a national observance in 1949 by President Harry S. Truman.