Flat River may refer to:
Rivers Flat River (Northwest Territories), a tributary of the South Nahanni River Flat River (Louisiana) Flat River (Missouri), a tributary of the Big River Flat River (Michigan) Flat River (North Carolina) Flat River (South Branch Pawtuxet River), a river in Kent County, Rhode Island Flat River (Wood River), a river in Kent and Washington County, Rhode Island
Inhabited places Flat River, Missouri, the former name of Park Hills, Missouri