Monument at Washington Monument State Park in MD

This is the first monument dedicated to George Washington to be completed; it was dedicated on July 4, 1827.  At the time it was only 1/2 completed; it was actually completed later in that year.  The monument is in the Washington Monument State Park outside of Boonsboro, Maryland.  It also sits along the Appalachian Trail at South Mountain.

While the tower is impressive in its own right, it also has significance in the Civil War.  The Battle of South Mountain took place at this site 3 days prior to the Battle at Antietam.  The tower was used by Federal signalmen during the battle (as well as the one in Antietam).  The park has a museum (of sorts) dedicated to the Battle of South Mountain.