The earliest record of any Thrale is thought to John Thral in the 1309 Subsidy Rolls [3] for Bedfordshire and William le Thral in the 1332 Subsidy Rolls for Sussex.1
Links
[1] http://www.thrale.com/user/login?destination=comment/reply/315%23comment-form
[2] http://www.thrale.com/user/register?destination=comment/reply/315%23comment-form
[3] https://en.wikipedia.org/wiki/Subsidy_roll
[4] http://books.google.co.uk/books?id=fPoujUPs3hYC&pg=RA1-PA445&vq=thrale&dq=The+Origins+of+English+Surname.+P.H.+Reaney.&source=gbs_search_s