In 1878, Simonds joined Jenney's architectural practice in Chicago. His first project was Graceland Cemetery where he learned naturalistic English-style landscape design. Through Jenney's tutaledge, he learned how to use native plants in landscape design, an unusual practice at the time. He studied local woods, hydrology, and topography leading him to be credited with the creation of the Prairie Style along with Jens Jensen, and Walter Burley Griffin. In 1880, Graceland was increasingly deferring to Simonds about the amount of work and money required to develop the property's eastern section before Jenney which led to ending Jenney's involvement in the project. This led to Simonds establishing the firm of Holabird & Simonds to carry out the work. In 1881, Martin Roche, who had also worked in Jenney's office, joined them as a third partner. In 1883, Simonds left the firm to concentrate solely to become the superintendent at Graceland. His work at Graceland led him to be called the "dean of cemetery design." In 1897, he left his position at Graceland but continued to be their landscape consultant for the rest of his career. In 1900, the cemetery was awarded a silver medal at the Exposition Universelle in Paris for its landscape and later a Medal of Honor by the Architectural League of New York in 1925.