The Illinois Geographic Center was the brainchild of Gary Calvert, who in 1991-1992 was taking classes at a business school in Rapid City, South Dakota. He later claimed to have visited a geographical center close to the United States monument that had fallen into oblivion — possibly the abandoned Geographic Center of the 49 states — and decided that a similar central monument for his home state could fill that gap and be a blessing for his fledgling career in tourism marketing. Calvert traveled to Chestnut, showed them his official letter from the Illinois State Geological Survey, and convinced the small community that it needed a monument, not in the exact place, which was in a bean field, but next to the state road that crossed the city. However, the exact center of Illinois is about eight miles southwest of Chestnut and, on the other side of the town of Mount Pulaski, 89°18.4'O 40°0.8'N.
David Clark mapped out the town of Chestnut in 1872 together with the directors of the then newly completed Gilman, Clinton and Springfield (later the Springfield branch of the Illinois Central Railroad). Calvert got a large map of Illinois, crossed it with a fishing line, and the lines converged near the village of Chestnut. He then contacted the Illinois State Geological Survey and, to his satisfaction, found that their calculations were similar to his own.
