Indian Lake (formerly "Lewistown Reservoir") is a reservoir in Logan County, western Ohio, in the United States. It is approximately southeast of Lima. It is fed by the north and south forks of the Upper Great Miami River, Cherokee Mans Run, Blackhawk Creek, and Van Horn Creek. The outlet of the lake, at the bulkhead or "spillway" (located at what is now State Route 366) built in the 1850s by Irish laborers, is the beginning of the Great Miami River. At , Indian Lake is the second largest inland lake in Ohio.