In this work we report a structural and compositional study of ferromagnetic In0.78Mn0.22Sb films correlated to the magnetic properties as determined by superconducting quantum interference device magnetometer. The epilayers grown by metalorganic vapor phase epitaxy on GaAs(001) substrates showed two active magnetic components with Curie temperatures of approximately 300 K and in excess of 570 K. Secondary phases driven by the high manganese concentration (10 at. %) were identified by high-resolution (scanning) transmission electron microscopy imaging and energy dispersive X-ray spectroscopy. Most of the Mn was found to be incorporated in metallic manganese nanoprecipitates surrounded by an InMnSb matrix with Mn at 1 at. % concentration. The origin of the two Curie temperatures of the film is associated with the presence of three magnetic components: hexagonal MnSb nanoprecipitates, non-stoichiometric MnAsSb, and the InMnSb matrix.