Guillaume [I] Goët succeeded in uniting the five baronies in the area known as Perche-Gouet: Authon, Bazoche, Montmirail, Alluyes and Brou, which were fiefs of the abbey of Saint-Père de Chartres[1258].
GUILLAUME [I] Goët (-before 1059). Seigneur de Montmirail. m as her first husband, MATHILDE d'Alluyes, daughter of GAUTHIER d'Alluyes & his wife --- (-after 1079). Her parentage and two marriages are confirmed by the charter dated to [1050/60] under which "Hugo…castri Breietelli possessor in pago Cenomannensi" donated "ecclesiam…in Dunensi pago…Lazellam" to Marmoutier, with the permission of "domine mee Mahildis filie Galterii de Aloia filiorumque ac filiarum eiusdem, quibus patres fuere Guillelmus cognomento Gugetus et Gauffredus de Medana…Willelmi, Hildeburgis et Richildis, item Hamelini, Galterii et Hersendis"[1259]. She married secondly Geoffroy [II] Seigneur de Mayenne. "Guillelmus Gogietus et mater eius Mahildis" donated property "ex bosco ipsorum de Pertico" with the consent of "Eustachia coniuge sua et filiis Guillelmo et Hugone" by charter dated 1079, witnessed by "Rodulfus filius Rotrochii bastardi"[1260]. Guillaume [I] & his wife had [four] children: