Courtalain fell to Eudes III Borel in the 12th century. In the 15th century, Guillaume d'Avaugour, king Louis XI's butler, replaced the old medieval fortress by a brand new castle, in 1493.
Then the castle fell to Guillaume de Montmorency (famous constable Anne de Montmorency's father) by marriage, in the 16th century. The estate stayed in this family until... the 19th century! In 1730, they put the architect Gabriel de Lestrade (Gabriel's disciple) in charge of raising new buildings and redecorating the apartments.
Anne-Léon de Montmorency, during the French Revolution, was exiled in England: Courtalain was sold. His son Anne-Charles owned it in 1813: Louis-Martin Bertault, the famous landscaper of the Malmaison (nicknamed the "Le Nôtre of the 19th century"), laid out a landscaped garden. Then few years later, the last duke of Montmorency completely restored the castle.