In 2018, Iowa produced 4.21 billion gallons of fuel ethanol—26% of the 16 billion gallons produced in the United States—according to the US Energy Information Administration (EIA).
Fuel ethanol is used as an oxygenate in gasoline and to produce E-85 fuel.
Other Midwestern states that produced more than one billion gallons were Nebraska, Illinois, Minnesota, Indiana, and South Dakota. In all, twenty-five states produced fuel ethanol in 2018.
Source: US Energy Information Administration, State Energy Data System (SEDS): 1960-2018, June 2020.