He married, firstly, an unknown wife. He married, secondly, Margaret, Countess of Buchan, daughter of Fergus, 4th Earl of Buchan, before 1210. He died in 1233.
William Comyn, Earl of Buchan held the office of Justiciar [Scotland]. He founded the Abbey of Deer in Buchan. He gained the title of Earl of Buchan, in right of his wife.
Child of William Comyn, Earl of Buchan
* Lady Idoine Comyn
Children of William Comyn, Earl of Buchan and unknown wife (?)
* Richard Comyn
* Walter Comyn, Earl of Menteith
* Sir John Comyn of Badenoch
Children of William Comyn, Earl of Buchan and Margaret, Countess of Buchan
* Elizabeth Comyn d. c 1267
* Alexander Comyn, 6th Earl of Buchan d. b 6 Apr 1290
William Comyn 
