The late 1950s brought extensive redecoration to Oldfields. The Lillys undertook decorative work throughout the house, including scenic and trompe l'oeil wall paintings by Canadian muralist Douglas Riseborough. Highlighting the new rooms was a collection of portraits by painters such as Nattier, Fragonard, Reynolds and Goya. Many of these were later purchased from the Lilly estate by Herman C. Krannert and donated to the Indianapolis Museum of Art; some are now on view in the galleries.
Mrs. Lilly died in 1965 and Mr. Lilly died the following year. Oldfields was given to the Art Association of Indianapolis by their children, Ruth Lilly and J. K. Lilly III, to serve as the new site for the museum. In 1970, the newly renamed Indianapolis Museum of Art opened to the public at its new location.