He was born in Cambridge, England [in 1291?]. He married Isabel [Isobell] de Newton in 1314. She was the eldest daughter and coheir of John [or William?] Newton, of East Newton, and brought the estate of East Newton into the Thornton family. William died in 1333. His tomb remains at Stonegrave church:
"From 1300 to almost 1700 the north aisle was the burial place of the Thornton family of East Newton but only two of their tombs remain. The tomb nearest to the tower, probably that of William Thornton (d. 1330), carved in York, is unusual in having the effigy of a civilian with legs crossed. The other, of Robert Thornton and his wife (d. 1418), is of local stone and workmanship. It is now in a recess in the north wall, the canopy formed from an earlier Easter sepulchre. The tomb chest has figures supporting shields showing the simple coat-of-arms of the family at that time - three thorn sprays. These effigies are all that remain of many memorials, silent figures watching over the building that the Thornton's had helped to maintain."
