We tabulated flowering plant species visited by 98 species of Lepidoptera as extracted from records of C. Robertson, who observed >15,000 insect visitors of flowering plants in central Illinois during a 33-yr period. Diversity of Lepidoptera was highest on plant species of the Asclepiadaceae and Verbenaceae, and the greatest number of lepidopteran species visited Verbena stricta Ventenat (Verbenaceae), Aster pilosus Willdenow (Asteraceae), Cephalanthus occidentalis L. (Rubiaceae), and Pycnanthemum flexuosum (Walter) Britton, Sterns, Poggenberg (Lamiaceae). Lepidopterans were particularly abundant on A. pilosus and C. occidentalis. The most polyphagous lepidopteran species were Colias philodice Godart (Pieridae), Danaus plexippus (L.) (Danaidae), Artogeia rapae (L.) [=Pieris rapae (L.); Pieridae], Phyciodes tharos (Drury) (Nymphalidae), Polites themistocles (Latreille) (Hesperiidae), Pontia protodice (Boisduval & LeConte) (Pieridae), and Everes comyntas (Godart) (Lycaenidae), each of which visited flowers of 50 or more plant species. Colias philodice, Phyciodes tharos, and Pontia protodice were the most common species. Most lepidopteran species evidently visited a limited range of nectar plants, which may have implications for species conservation and selecting “butterfly plants” for gardening.