Tack said there were 93 campers and 25 staff members at the camp.
About 40 people were injured, Sheri Bauwens, a nurse with the American Red Cross, said.
"Many of the injuries happened when a brick fireplace in one shelter was ripped apart by the storm. The shelter was one of four where scouts had run for cover," she said.
Lloyd Roitstein, president of the Boy Scouts of Mid-America Council, said the scouts at the ranch were advanced scouts between 13 and 18 years old and were there for a week of training.
He said they were staying in tents and that the site was destroyed.
"All of the buildings are gone; most of the tents are gone; most of the trees are destroyed," Roitstein said.
"You've got 1,800 acres of property that are destroyed right now.
The twister struck as Iowa, like other mid-western states, was dealing with severe flooding along the upper Mississippi River.
Heavy downpours hit the region over the weekend, with more thunderstorms predicted for Wednesday night and Thursday morning.
Flooding in the Iowan capital city of Des Moines and in other areas prompted mandatory evacuation orders and sandbagging in the state.
Tornado warnings were issued in areas stretching from Kansas to Minnesota.