In mid-December, 1929, Eli Lilly wrote to his eleven-year-old daughter, Evie, then living with her mother in Massachusetts. Like many of his letters to her, this one was filled with expressions of love for his only child and sprinkled with news of daily life that he hoped would interest her. This time he promised also a special project for their annual summer visit to Lake Wawasee. "Your Daddy has been having a lot of fun lately browsing in the State Library studying the history of the country around the lake. Lots of stories of old Indian chiefs." And, he promised Evie, "it will be lots of fun to see these places." In fact he was going to see "if there isn't an unopened Indian mound near the lake. If there is we will try to make arrangements to open it up next summer. Mr. [E. Y.] Guernsey, who knows all about those things and who visited us a day or so ago will tell us just how it should be done." At Wawasee in mid-1930 Lilly followed through on his promise. Although he and Evie did not find an Indian mound that summer they did visit with J. P. Dolan, a Syracuse lawyer who had a large collection of Indian artifacts.

Evie never developed an interest in archaeology. Her father soon became passionately engaged in the study of prehistoric peoples. A forty-five-year-old man whose adult life heretofore had been spent largely in single-minded devotion to the pharmaceutical business now discovered a variety of interests that led to wider horizons His success at Eli Lilly and Company in the 1920s, his termination of an unhappy marriage in 1926, and his joyful marriage to Ruth Allison in 1927 were followed by an unfolding of character and an expansion of interests that indicated a major shift in his life. Lilly remained a man of business, of course. He took great pride in the company his grandfather had founded and in his own opportunity to succeed his father as president in 1932, but the pill factory no longer consumed his every moment. Indeed, he complained to an archaeology friend in 1933, "I should like very much to be able to consider jumping my job here permanently and go digging, but unfortunately it seems impossible." And on another occasion he lamented, "I am so busy with Sales Managers this week that it will be impossible to have any fun at all." Devoted to his duty, Lilly stayed at the task on McCarty Street, even after his retirement from the presidency in 1948, but other challenges attracted an increasingly substantial portion of the time and intellectual energy he once devoted to business.

Lilly's interest in prehistoric archaeology began with Indian artifacts. Like many amateur collectors, he was fascinated by the projectile points, blades, pottery, figurines, and other artifacts that were readily found in many parts of America. Lilly followed his summer visit to Dolan and his "Indian cabinet" with a visit to the collections of the Smithsonian Institution and the Ohio State Museum in November, 1930, after which he exuded that he had "practically gone archaeology!" With the advice of Thomas Hendricks, an enthusiastic Indianapolis collector, he began building his own archaeology collection, eventually spending over $20,000. By early 1931 he owned all manner of artifacts and "several hundred problematical forms, including nearly a hundred birdstones." Birdstones were particularly attractive; not only were they a delight to the eye but, because their purpose was, and remains, unknown, their mystery attracted the imagination as well. Lilly early on decided to specialize in problematical forms.

As other collectors became aware of the Indianapolis businessman's new interest they wrote offering items for sale. The collection grew. In the new house he and Ruth built on Sunset Lane, birdstones, pottery, axeheads, and gorgets took over the third floor ballroom. In 1932, soon after moving into the new house, Lilly wrote a dealer that his architect had warned him that "if any more weight is piled into the attic it is likely to smash the house, so I am not buying any more relics from anybody." It was not the weight of the collection that stopped his purchases, however, but rather his evolution from a Saturday afternoon collector to a serious student of archaeology.