At the Midwestern Climate Center, a comprehensive re-evaluation and updating of heavy rainstorm frequency relations for 9 Midwestern states is in progress. A special effort is being made to determine the existence of climatic fluctuations and trends in heavy rainfall distributions since the start of this century, and their significance on frequency distributions that are a major input to the design and operation of flood control systems and other hydraulic structures. A second major objective is to provide better definition of spatial variations in extreme rainfall events. This paper largely focuses on the recently completed Illinois study with respect to problems encountered, analytical methods employed, results to date, and the significance of the findings. Preliminary results of the larger study area are also presented.