Lynda Herndon, do you have any more information about the William Thornton that you are looking for? Your post gives no clues to be able to identify the correct William. How much do you know about him? If you are having no luck tracing him back to Yorkshire then another option you may want to consider is Northumberland. The Thornton family was prominent in the Netherwitton and Hartburn area for several centuries. Unfortunately, they made some critical decisions on which side to support in major conflicts and lost lands and lives as a result. Quite possible that these events (Jacobite Rebellion and Civil War) and the subsequent effect on family fortunes may have been a trigger for sons to emigrate.