The calculated distance (air line) between Montdidier and Cergy-Pontoise is approximately 48 miles respectively 77 kilometers.
By car or train, the actual journey to Cergy-Pontoise is certainly longer, as only the direct route (as the crow flies) between Montdidier and Cergy-Pontoise has been calculated here.
Air line (approximately)
77 kilometers
41 nautical miles