Hennepin is a small unincorporated community along State Highway 7 in extreme southern Garvin County, Oklahoma, United States, near the meeting of the Carter, Garvin, and Murray county lines. The Hennepin Post Office was opened February 16, 1885, by Henry C. Dent in the old Chickasaw Nation of Indian Territory. It was named for Father Louis Hennepin, a member of Lasalle's Louisiana Expedition. The Hennepin ZIP Code is 73444.