The calculated distance (air line) between Monthey and La Chaux-de-Fonds is approximately 59 miles respectively 95 kilometers.
By car or train, the actual journey to La Chaux-de-Fonds is certainly longer, as only the direct route (as the crow flies) between Monthey and La Chaux-de-Fonds has been calculated here.
Air line (approximately)
95 kilometers
51 nautical miles