Alison was the daughter of Thomas FitzWilliam but her mother is unknown. The date and place of her birth have not been found.
She had two marriages/partners. Her first husband was Christopher Ussher. They were married, but the date and place have not been found. Their only known child was John (1524-c1590).
Her second husband was sir James FitzSimon. They were married, but the date and place have not been found. Their only known child was Catherine (?-1617).