This is an interesting topic. I once found myself in an argument with a Texan. I said Houston was named after Houston, Renfrewshire, Scotland. He said Houston was named after Sam Houston. We are, of course, both correct. Sam was, as you are, descended from Scots-Irish, Ulster Scots, who were descended from Lowland Scots who emigrated to Ireland with government assistance in the 17th century. I sometimes watch American Football and a large proportion of the players run around with Lowland Scottish names on their backs. It is not the fact that they have Scottish names that is striking. It is that there are very few Highland names. No Mac's.
From news coverage, I have learned that there is a Crawford in Texas where one of your former presidents hangs out. I have no idea whether or not, that place is named after someone whose surname was Crawford or if someone from the original village in Scotland named it. However, I do know the surname Crawford came before the Scottish village. It came from Normandy with the Norman invasion.
Similarly, you might have some detective work to do with your surname. Obviously, Hemphill is a geographical feature. Hemp is a plant, as I am sure you know. However, your forebears may have come from Hemphill at some point. If you try the 'Scotland's People website you might be lucky. Unfortunately, many parishes do not have adequate records for the 17th century. But, some do. Some go back to the 16th. Good luck.