The purpose of this brief is to update our previous evaluation of yield potential for corn in Illinois, Indiana, and Iowa in 2009. (Irwin, Good, and Tannura, 2009). This update makes use of a crop weather model that estimates the impact of technology (trend), state average monthly weather variables, and portion of the crop planted late on state average yield. Previously, that model was used to evaluate 2009 yield potential based on planting progress, state average precipitation through April 2009, and alternative 2009 summer weather scenarios. This update incorporates preliminary state average precipitation for June and alternative weather scenarios for July and August 2009. The yield forecasts for the three states are then used to project the U.S. average yield. Trend yields for 2009 for each of the three states and the U.S. are also presented.