In 1799 Pratt purchased 43 acres (17 ha) of "The Hills" and accompanying structures at a sheriff's sale for $14,654 after occupant Morris suffered financial misfortunes and was taken to debtors' prison.

[3] Pratt designed the house and supervised its construction,[4] though he did not live year-round at Lemon Hill: his primary residence was in a townhouse on Front Street.

[5] To protect its water supply, the City of Philadelphia began purchasing properties along the Schuylkill River, beginning with Lemon Hill in 1844.

Kimball conjectured that Robert Morris had built the mansion; however, in 2005, Pratt's letterbooks were found at the William L. Clements Library of the University of Michigan, Ann Arbor by an assistant curator of the Art Museum.

Long hidden by dense trees on the sides of the hill, a restoration of the historic views was undertaken in 2007, recreating the original vistas of, and from, the mansion.