Flat Rock is an unincorporated community in Washington Township, Shelby County, Indiana. Flat Rock was platted in 1855. The community took its name from the Flatrock River. Flat Rock had its own high school at the turn of the 20th century. Flat Rock is located at 39°21′51″N 85°49′54″W / 39.36417°N 85.83167°W / 39.36417; -85.83167.