During the Hundred Years War, the English occupied the Vexin from 1419 to 1441. Groux sheltered partisans of the Dauphin Charles and brigands who resisted the invaders. Peasants were used as liaison officers. During this century most of the grounds of Liancourt belonged to the Malherbe family.
After the death of Robert de Malherbe, it is his nephew Charles de Pellevé who acquire from the king in 1537 the high, average and low justice rights of the parishes of Liancourt, of the hamlets of Vaux, Launay, Vivray.
Armorial bearings of Pellevé
Liancourt was then governed by the habit of Senlis, regulated in 1539, under the reign of François 1st. It depended on the baillage of Chaumont, itself a part of the baillage of Senlis. The baillage of Chaumont had been set up in 1543. It, in 1563, was divided into two seats, of which one returned to Chaumont and the other to Magny.
François 1st (1494-1547)