This paper estimates returns to scale and technical efficiency of corn farms following an input distance function approach and compares the relative performance of farm operator households with and without off-farm wages and salaries. We use 1995-2003 USDA data. The input distance function results suggest that off-farm outputs and inputs can be modeled in a multi-activity framework, which materially alter performance measures in the Corn Belt. We find that off-farm income boosts scale and technical efficiency of smaller operations. We also find that the number of hours worked off-farm by the spouse contributes to a higher technical efficiency.