In 1863 he enlisted in the 86th Ohio Volunteer Infantry, but continued his artistic pursuits through his illustrations of the Civil War. During this time he became friends with the Cleveland photographer and entrepreneur, James F. Ryder. Ryder convinced Willard that they could have a profitable partnership selling Willlard's work and he soon began selling photographic copies of Willard's drawings.
After the war Willard continued to collaborate with Ryder, creating comic chromolithographic prints that Ryder sold. The royalties from these sales were enormous and provided Willard with the means to travel to New York to study with fellow Ohioan, Joseph Oriel Eaton. Willard's talent was quickly recognized, and he exhibited at the National Academy of Design the next year.
When Willard returned to Cleveland in 1875 he opened a painting studio and renewed his partnership with Ryder. At about this time he began work on "Yankee Doodle" (later known as "The Spirit of '76") for the upcoming Centennial Exposition in Philadelphia. The painting was displayed in Memorial Hall at the exposition and Ryder sold chromolithographs of the image to promote the exhibit.
It was the success of this exhibition that established Willard's fame and in later years he was asked repeatedly to make replicas of the painting. Willard also became active in the Cleveland arts community and was a founding member of the Cleveland Arts Club. He continued to paint and exhibit his work until his death in 1918.