The McCormick family's homestead of Walnut Grove was located near Raphine, Virginia, although they moved to Chicago in 1848 to manufacture the reaper on a large scale.

In 1870, Robert E. Lee, who was then president of Washington College, sent a letter of introduction to Joseph Henry, secretary of the Smithsonian Institution, making known McCormick's wishes to establish an astronomical observatory in the state.

However, the Clarks made some adjustments to the lens to improve the image quality over that of the Naval Observatory refractor.

Starting in 1914 the second director, Samuel Alfred Mitchell, began a program to measure the distances to nearby stars (stellar parallax) using photography.

This program continued under the next two directors, Harold Alden and Laurence Fredrick; over the course of more than 80 years, the distances to thousands of stars have been determined with the McCormick Refractor.

Peter van de Kamp, Alexander N. Vyssotsky, Emma T. R. Williams and Dirk Reuyl also carried out research on the number and types of stars seen in different directions, and from this deduced information about the size and shape of the Milky Way.