The non-instrument-rated pilot stated that prior to departure, weather reports indicated that clear sky conditions prevailed at the departure airport with areas of fog at his destination. Despite the possibility of fog at his destination, he decided to attempt the flight with the intention of diverting to an alternate airport if the weather conditions deteriorated. While en route over mountainous terrain, he observed fog encroaching the foothills near the destination airport. The pilot attempted to listen to the airport’s automated weather observation system but could only discern the altimeter reading due to radio static. He initiated a descent to the traffic pattern altitude and observed fog approaching the airport’s perimeter. The pilot further stated that as the airplane was on the final approach path, about 3 miles from the airport, the visibility began to decrease. In an effort to maintain visual contact with the airport, he maneuvered the airplane below a fog bank and elected to continue the approach in instrument meteorological conditions. The airplane descended to about 500 feet above ground level and became surrounded by fog, resulting in the pilot losing visual reference. Shortly thereafter, the airplane touched down in a plowed field and rolled onto its right side, sustaining substantial damage to the fuselage and the right wing. Weather records revealed that at the time of the pilot’s initial weather briefing, the destination airport was reporting instrument meteorological conditions. The accident occurred just before dusk. The pilot reported no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation.