Please anyone, correct if wrong on this. I believe it is sugar cane that is the main source for ethanol. Not sure where this is grown in the US.
Here is something I found on a Dept. of Energy website.
Ethanol is a clear, colorless alcohol fuel made from the sugars found in grains, such as corn, sorghum, and wheat, as well as potato skins, rice, and yard clippings. Ethanol is a renewable fuel because it is made from plants. There are several ways to make ethanol from biomass. The most commonly used processes today use yeast to ferment the sugars and starch in corn. Corn is the main ingredient for ethanol in the United States due to its abundance and low price. Most ethanol is produced in the corn-growing states in the Midwest. The starch in the corn is fermented into sugar, which is then fermented into alcohol. Other crops such as, barley, wheat, rice, sorghum, sunflower, potatoes, sugar cane and sugar beets can also be used to produce ethanol.
http://www.eia.doe.gov/kids/energyfacts/sources/renewable/ethanol.html
This is probably more specific answer.
The U.S. corn market will continue to be dominated by ethanol production in the coming year. Ethanol corn use for 2008/09 is projected to increase 28 percent and account for 31 percent of total corn use as ethanol production capacity continues the unprecedented expansion begun in 2006.
PROSPECTS FOR THE U.S. FARM ECONOMY IN 2008
Joseph Glauber, Chief Economist,USDA
http://www.usda.gov/oce/forum/2008Speeches/PDFSpeeches/Glauber.pdf
Ethanol Production Continues to Drive Corn Market