On August 4, 2000, at 1715 central daylight time, a Bell 206B, N7JR, was substantially damaged on impact with terrain during a practice emergency autorotation from an altitude of 30-40 feet agl at a private heliport near Marengo, Illinois. Visual meteorological condition prevailed at the time of the accident. The 14 CFR Part 91 personal flight was not operating on a flight plan. The pilot sustained serious injuries. The local flight originated from the private heliport at 1600. In a written statement, the pilot reported the following,: "The flight originated at IL 68 RLA, Barrington, IL, Friday, August 4, 2000, at approximately 1600 local time." "I flew to Wind Rose (Krause) RLA, located just SW of Routes 23 and 90 in Marengo, IL. At this location is a 2900' x 300' grass airstrip. I am the owner of both RLA's. "I flew to Marengo to practice auto rotations from flight in preparation for recurrent training, scheduled with an instructor the next day." "I began the first auto rotation at 1500' AGL and recovered at approximately 50' with an engine recovery. The second auto rotation was the same as the first." "The third auto rotation was begun at 500' AGL keeping the two needles close together with a forward arispeed of 60 mph. The auto rotation proceeded normally until flareout and recovery of the flareout at 50', at which time the needles split and I descended at a rapid rate to the ground. The helicopter came to rest in a flat postion with the landing skids splayed but level and upright. "Weather conditions were good: Wind 0; Temperature 85 F; Ceiling unlimited; Visibility 10 miles." The pilot's safety recommendation was, "Begin auto rotation from a higher altitude". According to a statement by a Federal Aviation Administration Inspector, "...[The pilot] stated that he had completed two autos from approximately 1500 AGL with power recovery without incident. [The pilot] then stated that he did the next auto at a LOW altitude. He would not say what that altitude was. He did say the helicopter was at a near zero airspeed when he initiated it."