The Rauner administration said in a prepared statement that it "accepted the resignation" of Nelson on Thursday. The statement said Buchen "had also stepped down."
Buchen called the situation "political crap."
"I resigned because they fired (Nelson), and it's just a bunch of bull crap," Buchen said.
Nelson could not be reached for comment.
In the statement from his office, Rauner said: "I appreciate Director Nelson's commitment to agriculture and his service to the people of Illinois. I wish him all the best."
Nelson will remain with the department for another 30 days to help with the transition to a new director. Rauner's office said the search for a new director is underway. In the meantime, Warren Goetsch, chief of staff at the Agriculture Department, will serve as acting director.
Rauner tapped Nelson in January to be the new agriculture director. Rauner had said he wanted someone with a farm background to lead the department,
Sen. John Sullivan, D-Rushville, chairman of the Senate Agriculture Committee, said he'd heard nothing of Nelson's departure.
"It just hit me in the gut," Sullivan said. "There's nobody higher in ethics and morals than Philip Nelson. I can't imagine why they would ask him to resign or fire him or whatever. I would think the ag community would be very upset by this."
Buchen was named fair manager in May, replacing Amy Bliefnick. Buchen, a Fulton County native, had previous experience running the Indiana State Fair and was president of a company that staged garden and holiday shows around the country.
He was hired at a salary of $120,000 to run both the main state fair in Springfield and the Du Quoin State Fair. Previously, the fairs had separate managers.
Buchen stirred controversy when he announced attendance at the state fair this year was this year was about 411,000, less than half the 844,000 from a year ago. At the same time, he said, fair revenues were about the same.
Buchen said he used a different method to calculate attendance that is widely accepted by the fair and exposition industry. He suggested that crowd estimates used previously by fair officials were inflated.
Illinois Ag Director, Du Quoin and Springfield Fair Manager Resigns
updated: 9/24/2015 11:42 PM