On July 25, 2016, about 1050 central daylight time, a Texas Helicopter OH-13H/M74A, N10009, was substantially damaged when it was struck by a passing semi-trailer truck during reloading operations near Minonk, Illinois. The pilot, loader, and truck driver were not injured. The helicopter was registered to and operated by Hendrickson Flying Service, Rochelle, Illinois, under the provisions of Title 14 Code of Federal Regulations Part 137 as an agricultural application flight. Visual meteorological conditions prevailed, and no flight plan for the local flight had been filed.The agricultural application nurse truck was stationary and parked on the right shoulder of a paved rural county road, facing west, and was completely clear of the roadway surface. According to the loader, the nurse truck's hazard lights were on. The helicopter was parked on the elevated helipad on top of the nurse truck with the helicopter's engine operating and the rotor blades turning. The nose of the helicopter faced north, and the helicopter's tail boom and rotor disk extended about 8-10 feet over the road. The loader stated that he was reloading the helicopter's product tanks when a westbound semi-trailer truck drove underneath the rotor disk and struck the helicopter's tail boom. The impact turned the helicopter 20-30° from its position on the helipad. The helicopter remained upright and on the top of the helipad. The right side of the cab and the cargo cover and frame to the truck trailer were damaged. The truck driver told a Federal Aviation Administration (FAA) inspector that he thought he had enough clearance to pass safely under the helicopter's tail rotor. He maintained that the accident was not his fault. The pilot was asked why the truck was positioned so that the helicopter's tail boom was extended 10 feet over the highway. He replied that if he had parked closer to an adjoining field, the platform would have a tilt, making it difficult to land for servicing. The loader provided a statement and said that, in the future, if loading operations need to occur off a well-traveled road, they would take measures to ensure the tail boom is not over the main road. After examining the accident site, the inspector noted that were other flat areas in the vicinity but considered too far from the field being sprayed. The inspector also noted that the tilt would not have been significant or impeded the highway.