Numerous controlled experiments find that elevated ground-level ozone concentrations ([O-3]) damage crops and reduce yield. There have been no estimates of the actual yield losses in the field in the United States from [O-3], even though such estimates would be valuable for projections of future food production and for cost-benefit analyses of reducing ground-level [O-3]. Regression analysis of historical yield, climate, and [O-3] data for the United States were used to determine the loss of production due to O-3 formaize (Zeamays) and soybean (Glycine max) from 1980 to 2011, showing that over that period production of rain-fed fields of soybean and maize were reduced by roughly 5% and 10%, respectively, costing approximately $9 billion annually. Maize, thought to be inherently resistant to O-3, was at least as sensitive as soybean to O-3 damage. Overcoming this yield loss with improved emission controls or more tolerant germplasm could substantially increase world food and feed supply at a time when a global yield jump is urgently needed.