The calculated distance (air line) between Château-Thierry and Paris 18 Buttes-Montmartre is approximately 49 miles respectively 79 kilometers.
By car or train, the actual journey to Paris 18 Buttes-Montmartre is certainly longer, as only the direct route (as the crow flies) between Château-Thierry and Paris 18 Buttes-Montmartre has been calculated here.
Air line (approximately)
79 kilometers
43 nautical miles