On July 6, 1997, at 0845 central daylight time, a Cessna 182R, N661SP, operated by the Illinois State Police, collided with the terrain and a sign post during a forced landing following a loss of engine power. The airplane was on final approach to runway 31 at the Greater Peoria Regional Airport, Peoria, Illinois, when the loss of power occurred. The commercial pilot reported minor injuries. Visual meteorological conditions prevailed. The airplane was substantially damaged. The public use flight originated from Springfield, Illinois, at 0815 cdt. The pilot stated that he had the power reduced during his approach to land. When he advanced the throttle to add power, the engine power did not change. There was not increase or decrease in power. Due to obstacles between his position and the runway he elected to make a forced landing in a soybean field just north of the approach path for runway 31. He reported he touched down in the field but it was too short. The airplane contacted a ditch at which time the nose gear collapsed. The airplane continued across a road and came to rest after contacted two sign posts. Post accident inspection of the engine by a Federal Aviation Administration Inspector failed to reveal any malfunction/failure which would have prevented normal operation of the engine although it was noted that the spark plugs were sooted. The engine was later test run by the Illinois State Police who reported that it started and ran without interruption. According to a carburetor icing probability chart, the temperature and dew point, 68 degree F. and 56 degrees F. respectively, present at the time of the accident were conducive to moderate icing at cruise power or serious icing at glide power.