In 2005, the National Park Service took over ownership and management of Washington Square, through an easement from the City of Philadelphia.

[2] Originally divided into triangles by two creeks, the northwestern portion was the potter's field, and the southeastern section was for the burial of Catholics.

[3] The joining of the creeks created a fishing pond, and the grounds were commonly used for grazing by neighbors' cows.

Long mass grave trenches the width of the square were first dug along 7th and Walnut Streets, and were eventually expanded to the South side.

Many victims of the city's yellow fever epidemic of 1793 were interred here, and the square was also used for cattle markets and camp meetings.

[5] An unknown number of bodies remain buried beneath the square and the surrounding area; some are still occasionally found during construction and maintenance projects.