Following the 1888 acquisition of the Ellarslie Mansion and surrounding lands which were designed by John Notman, the City of Trenton consulted with Frederick Law Olmsted, Sr., in 1890 about redevelopment of the site as a public park. Design proceeded rapidly, much of it under the supervision of John Charles Olmsted, and a looping carriage drive, pathways, and plantings were quickly installed in the following years. The existing mansion was the focal point of the design, to be repurposed as a refectory, and new approach drives and paths provided connections to it. Complementing this structure were a vine-covered terrace and concert grove, which provided outlooks to the tree-dotted lawn beyond. In 1892, political changes in Trenton resulted in decreased support for parks, and Olmsted, Sr., lost the commission. While park progress continued to follow the broad contours of the Olmsted firm’s plan, monuments and zoo enclosures were introduced into the pastoral landscape against the firm’s recommendations.
Though they did not have direct influence over the park’s design during this period, Olmsted Brothers, in 1905, did implement a subdivision plan for the land opposite the park’s eastern edge, which their father had speculated on in the park’s initial planning. John Charles Olmsted prepared designs for the Cadwalader Heights property of businessman E. C. Hill with curving streets that extend the curvilinear character of the park’s drives out into the surrounding neighborhood, blending it into the rectilinear grid of the city. In 1910 the firm was again retained to work on the park, this time to design an addition to the south, which included a wading pool for children, tennis courts, and refinements to the approach to the main park. The Mansion House was listed in the National Register of Historic Places in 1973, with little reference to the park.