On August 5, 2017, about 1000 eastern daylight time, a Cessna 140, N89738, was substantially damaged during a forced landing following a total loss of power near Mount Sterling, Kentucky. The private pilot sustained serious injuries. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed for the local flight that departed Stanton Airport (I50), Stanton, Kentucky.The pilot reported that he departed from I50 with about 9 gallons of fuel in the left tank and 12 gallons in the right tank, and with the fuel selector positioned to the left fuel tank. About 20 minutes into the flight, while flying at an altitude of 2,400 ft with the engine operating at 2,400 rpm and the mixture leaned, the engine experienced a total loss of power. He made a forced landing in a field, and after touchdown the airplane went over a fence and down a hill before impacting a creek. Before exiting the airplane he turned off the "…master switch, fuel, radio, and ignition." Postaccident examination of the airplane by the FAA inspector revealed substantial damage to the right wing and fuselage. The right fuel tank was full, about 12 gallons of fuel. The left tank had about 2.5 gallons of fuel. The fuel was free of water and contaminates. No fuel was found in the carburetor bowl. The fuel selector valve was intact and in the "OFF" position. The fuel tank vent caps were unobstructed. The engine's crankshaft was manually rotated by turning the propeller, and continuity of the crankshaft and compression was confirmed on all cylinders. The cylinders were examined using a lighted borescope and no anomalies were noted. All leads from the left and right magnetos produced spark when rotated by hand. The two-seat, high wing, tailwheel-equipped airplane, was powered by a Lycoming O-235, 116-horsepower engine. The last engine overhaul was completed on June 3, 1975. The pilot held a private pilot certificate with a rating for airplane single-engine land. He reported 1,200 hours of total flight experience on his most recent application for an FAA third-class medical certificate, which was issued on August 3, 2016. The 1255 weather at Mount Sterling Montgomery County Airport (I50), about 9 miles northwest of the accident site included wind from 100° at 6 knots; visibility 10 statute miles; temperature 22° C; dew point 11° C; and altimeter setting 30.18 inches of mercury.