Hennepin is a village on the Illinois River in Putnam County, Illinois. The population was 757 at the 2010 census and it is the county seat of Putnam County. Because of its location on the Illinois River, Hennepin has a large amount of industry. Marquis Grain, Inc. is responsible for the procurement of corn supplies to the Marquis Energy LLC ethanol plants in Hennepin, Illinois and Necedah, Wisconsin. They also provide distiller's grains marketing services for both plants. Dynegy operates power generating facilities in eight states in the Midwest, the Northeast and the West Coast. Hennepin is now Tri-Con Materials home base of operation and is the largest active gravel pit located on the Illinois River. Washington Mills manufactures and distributes a broad line of fused mineral products designed to meet the needs of your particular industry or application. There are also Cargill, ADM, and CGB elevators throughout the area.