From the park signs:

"Originally erected in 1827 by the citizens of Boonsboro, MD, the Washington Monument became the first completed monument dedicated to the memory of America's first president.
According to the legend, nearly the entire villatge of Boonsboro, some 500 people, trekked up South Mountain on July 4, 1827 to build and dedicate the Washington Monument. Constructed with granite found onsite, it took 2 days to build. It was originally built without mortar. Huge stones were carefully selected and accurately cut and then laid in the dry circular wall. Upon completeion it stood 30 feet high with a circumference of 54 feet at the base.
It became a popular meeting place.
It was used as a signal station during the Civil War by the Union. Weather, vandalism and neglect soon reduced it to rubble. So in 1882 the Odd Fellows Lodge of Boonsboro restored the monument, however, it quickly fell to ruin again.
In 1920 the Washington County Historical Society purchased the one-acre site and in 1934 it was deeded to Maryland as a state park. The CCC rebuilt the tower in its present form."

Deignated a NATIONAL HISTORICAL MONUMENT 1972