The 1905 completion of the McMillan Reservoir Sand Filtration Site was a Washington public health milestone. Its innovative system of water purification, relying on sand rather than chemicals, led to the elimination of typhoid epidemics and the reduction of many other communicable diseases in the city. The 25-acre site consisted of regulator houses, sand bins, washers and underground sand filtration beds. A legacy of the City Beautiful Movement, the complex was an engineering wonder that served its original purpose until 1986.

In 1906, Secretary of War William Howard Taft designated the site as part of the McMillan Reservoir Park, a memorial to Senator James McMillan, for his leadership as chairman of the Senate Commission on the Improvement of the Park System and in recognition of his work to shape the development of the city at the turn of the 20th century.

Conceived as a large permanent reserve of open green space for the benefit of citizens, the site’s design and construction was the collaboration of pre-eminent civil engineers, urban planners, artists and architects, including engineer Allen Hazen, planner and landscape architect Frederick Law Olmsted, Jr., sculptor Herbert Adams, and architect Charles Platt.

In 1991, the D.C. Historic Preservation Review Board designated McMillan Park a Historic Landmark and nominated the site for inclusion in the National Register of Historic Places.