Feb. 21, 1885: The Dedication of the Washington Monument On this day in 1885, the Washington Monument was officially dedicated. Three years later, it was opened to the general public. The Washington Monument lies in the center of Washington, D.C. and it commemorates the first president of the United States, George Washington. The monument was designed by Robert Mills and it was completed by Thomas Casey. Once construction was done, the Washington Monument was the world's tallest building, measuring 555 feet.  See how the Washington Monument and other iconic locations in Washington, D.C. have changed throughout the past 100 years. Top Photo: Washington Monument in 1860; Bottom Photo: Washington Monument in 1902 (Library of Congress).