Throughout his long life, Lilly took a personal interest in the history of Indiana and his hometown of Indianapolis. A man of significant personal wealth, whose philanthropic contributions were often given anonymously, Lilly was also modest, quiet, and unassuming. He made substantial gifts and actively supported the work of individuals and groups who shared his passions for archaeology, state and local history, art, religion, education, and civic improvement. In addition to his personal philanthropy, Lilly, with his father, Josiah K. Lilly Sr., and brother, Josiah K. Lilly Jr., established the Lilly Endowment, a philanthropic foundation that continues to support their family's generosity into the twenty-first century. Lilly also wrote, edited, or contributed to published works related to the prehistory of Indiana; Christ Church Cathedral, Indianapolis; the Delaware tribe's chronicle, Walum Olum; Indiana's Lake Wawasee; and archaeologist Heinrich Schliemann. A politically conservative Republican and a lifelong member of the Episcopal church, Lilly's traditional values concerning family, home, and community service guided his work in the pharmaceutical industry and in civic life.