Simon de St Liz, Earl of Northampton

Simon I de Senlis (or Senliz), 1st Earl of Northampton and 2nd Earl of Huntingdon jure uxoris (died between 1111 and 1113 [probably 1111 as this is when his castle at Northampton passed to the crown]) was a Norman nobleman.

In 1098 he was captured during the Vexin campaign of King William Rufus and was subsequently ransomed. He witnessed King Henry I’s Charter of Liberties issued at his coronation in 1100. He attested royal charters in England from 1100–03, 1106–07, and 1109–011. Sometime in the period, 1093–1100, he and his wife, Maud, founded the Priory of St Andrew's, Northampton. He witnessed a grant of King Henry I to Bath Abbey on 8 August 1111 at Bishop's Waltham, as the king was crossing to Normandy. Simon de Senlis subsequently went abroad and died at La Charité-sur-Loire, where he was buried in the new priory church. The date of his death is uncertain.

He built Northampton Castle, the town walls and one of the four remaining round churches in England, The Holy Sepulchre, Northampton.

Simon was the third son of Laudri de Senlis, sire of Chantilly and Ermenonville (in Picardy), and his spouse, Ermengarde.

He married in or before 1090 Maud of Huntingdon, daughter of Waltheof, Earl of Northumbria, Northampton and Huntingdon and better-connected Judith of Lens also known as Countess Judith, niece of William the Conqueror who had earlier refused to wed Simon and fled abroad to avoid William's wrath. They had three children:

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