Château-Thierry (shätōˈ-tyĕrēˈ) [key], town (1990 pop. 15,830), Aisne dept., N France, on the Marne River. The town was the focal point of the second battle of the Marne (1918), which ended the last German offensive of World War I. An imposing monument to the U.S. soldiers who fought in the battle is just outside the town. The birthplace of Jean de La Fontaine is preserved as a museum.