An amateur naturalist of Philadelphia, Willcox became a member of the Academy in 1867 and was later appointed curator of the Lea Collection of Shells. He was a member of the Board of Trustees of the Wagner Free Institute of Science, and Chairman of its Museum Committee for years.

This collection contains 33 letters signed by Willcox, many of them discussing the Academy, the Wagner Institute and natural history; a letterpress memorial card and a bound volume of plant impressions. The volume has 41 plates of unnamed plants, the impressions made directly from dried specimens. The latter were laid on freshly smoked paper and then transferred to clean sheets, the impressions being made under pressure.