On March 12, 2019, at 1442 central daylight time, a Piper PA32R-300 airplane, N750R, was substantially damaged during a forced landing following a loss of engine power near Waterloo, Illinois. The pilot sustained serious injuries, one passenger sustained minor injuries, and the second passenger, a child restrained in a car seat, was not injured. The airplane operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. The pilot reported hearing a "horrible noise" and the engine "immediately seized" about 10 minutes from the destination airport. Oil covered the windshield, obstructing his forward field of view. He executed a forced landing to a road by holding the airplane in a right crab to see out of the left side window. The airplane came to rest inverted in a grass area adjacent to the road with damage to the fuselage and both wings. A postrecovery engine examination revealed the No. 4 and No. 6 connecting rods had separated from the crankshaft. The no. 4 connecting rod was fractured through the upper rod yoke. The corresponding rod cap and bearing fragments were deformed. The no. 6 connecting rod was fractured across one side of the rod yoke; the opposite side was intact but deformed. The corresponding rod cap was deformed. The connecting rods remained attached to the pistons. The pistons were wedged within the cylinders. The pistons, lower cylinder flanges and connecting rods exhibited secondary mechanical damage. The crankshaft was intact. The crankcase was fractured above the No. 4 and No. 6 cylinders exposing a hole in the upper surface of the crankcase. Metallurgical examination was unable to determine source of the initial failure due to secondary mechanical damage. The intact fracture surfaces that were available for examination exhibited features consistent with overstress.