The origin of the name of the town is unknown. The local tradition attributes it to Thierry IV, the penultimate Merovingian king, who was imprisoned by Charles Martel, without a reliable source. Château-Thierry is the birthplace of Jean de La Fontaine and was the location of the First Battle of the Marne and Second Battle of the Marne. The region of Château-Thierry (the arrondissement, to be exact) is called the country of Omois. Château-Thierry is one of 64 French towns to have received the Legion of Honour.
During the 8th century, Charles Martel kept king Theuderic IV prisoner in the castle of Otmus. At this time, the town took the name of Castrum Theodorici, later transformed in Château-Thierry (Castle of Thierry, Thierry is the French or early Roman language translation of Theuderic).
Château-Thierry was the site of two important battles. The Battle of Château-Thierry (1814) in the Napoleonic Wars between France and Prussia, and Battle of Château-Thierry (1918) in World War I, between the United States and Germany.
In 1918, a mounting for the infamous Paris Gun was found near the castle. The cannon itself was never found.