Stealing a phrase from the "Hitchhiker's Guide to the Galaxy", there is still time to plant and get above average yields. The attached chart shows the Illinois corn planting progress chart since 1999 and the corresponding corn and soybean yields. I included the soybean yields because I have heard the question, "If corn planting is late, then soybeans will be even later and we have been pushing for early planting beans for higher yields." The USDA NASS data in the chart does not really show a penalty for years when things start really slow. At least on a statewide basis low yields have little relationship to April planting.

On the other hand, planting when the soil is not ready can lead to unrecoverable conditions such as sidewall compaction.