He was born in Montfort l'Amaury, near Paris, and became its lord.

He was the son of Amaury I de Montfort and Bertrade.

[1] At his death he was buried about 20 miles (32 km) away in Épernon, because it was the site of the fortress he was instrumental in constructing.

Simon I first married Isabel de Broyes (b.

1034 in Broyes, Marne),[2] daughter of Hugh Bardoul.