Although a hard-working businessman, Lilly eventually acquired diverse interests outside the pharmaceutical company. He nurtured a passion for prehistoric archaeology that led to significant scholarly publications and to financial and personal patronage that helped bring archaeology to professional maturity. Lilly researched and wrote history, preserved houses, and actively encouraged and sponsored the work of others.
During the last three decades of his life Lilly gave away millions of dollars personally and through the Lilly Endowment. Even more impressive than the large size of his philanthropy, however, was his personal involvement.