Midwestern agriculture is moving toward large, specialized production units where harvested crops are shipped off the farm and livestock are raised on purchased feed. Many people are concerned that increased manure concentration from specialized livestock units poses an unacceptable environmental risk. The unequal distribution of livestock production across counties in Iowa, Illinois, and Indiana suggests that a disaggregated analysis of crop nutrient use and manure nutrient supply is needed to estimate the risk of excess nutrient losses to the environment. The authors analyze nutrient use and supply at the county level.