On July 27, 2013, about 1030 eastern daylight time, a Cessna 175, N9388B, was substantially damaged during a runway excursion after landing at Windham Airport (IJD), Willimantic, Connecticut. The private pilot and two passengers were not injured. The airplane was registered to and operated by the private pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which originated from Salmon River Airfield (9B8), Marlborough, Connecticut about 1000. According to the pilot, the airplane’s tailwheel experienced a mechanical failure; however, no further comment was provided. According to an eyewitness, the landing “looked normal.” When the tailwheel made contact with the runway surface, he heard it “shimmy” and then watched the airplane depart the runway into the grass as a “classic ground loop.” The eyewitness further reported that the pilot attempted to taxi the airplane to the parking ramp after the runway excursion, until the pilot was signaled to stop by the eyewitness. The witness further reported that the tail of the airplane was placed in the back of his truck and the airplane was towed to the ramp. Postaccident examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed substantial damage to the left wing, elevator, and tailwheel. The left wing was crumpled on the outboard approximate 4 feet, the left elevator was crumpled, and the vertical stabilizer rear spar was cracked. The left side tailwheel mounting bolt was stripped and the wheel was angled to the right. Photographic documentation revealed that the tailwheel had little or no tread remaining, with the majority of the remaining tread on the outer rim of the wheel. Photographs provided by the FAA inspector did not show any abnormal wear on either sidewall of the tire that would be indicative of the tailwheel being angled to the right during touchdown. The main landing gear was inspected and no damage was observed. However, the pilot had disassembled the airplane, transported the airplane to his private residence, and began repairs prior to the inspector’s arrival on scene. Photographs provided by the FAA inspector revealed skid marks on the runway similar to those of a free-castering wheel as well as skid marks from the right main landing gear. The skid marks continued off the right side of the runway. However, since the airplane was removed from the location prior to any documentation, the skid marks could not be positively correlated to the accident airplane.