The non-certificated pilot reported that the airplane fuel tank contained one gallon of gasoline prior to departure. The pilot departed in his unregistered airplane on a local flight and monitored the fuel in the fuel tank line during the flight. He said the fuel line indicated that there was three inches of fuel in the fuel tank. The engine lost power about a half hour into the flight and one mile from its destination. The pilot made a forced landing on a cornfield, and the airplane sustained substantial fuselage damage. The pilot reported that there were no mechanical malfunctions with the airplane in reference to the accident flight. His safety recommendation stated that he should not have flown with so little fuel, and he should not have trusted the fuel level he saw in the line.