Hennepin is a village on the Illinois River in Putnam County, Illinois, United States. The population was 707 at the 2000 census. It is the county seat of Putnam County.
Hennepin is part of the Ottawa–Streator Micropolitan Statistical Area.
Hennepin is located at 41°15′24″N 89°19′48″W / 41.25667°N 89.33°W / 41.25667; -89.33 (41.256712, -89.329899).