Train localization in necessary to have a railway network both safe and efficient. This work presents an on board train localization system based on magnetic sensors. Previous works on magnetic train localization have achieved performances similar to GNSS localization. Besides, magnetic localization availability in not influenced by the local environment (as it happens for GNSS, e.g. in tunnels). During this work, a system based on multiple low-cost magnetic sensors has been designed, built and tested. The final result is the magnetic sensor array system: it does not require dedicated infrastructure features and can be used on trains up to 200 km/h.