I'm not so certain that Henry Butler/Boteler really is the father of your William Butler. Unfortunately, if William was indeed born in what is now Frederick, Maryland in 1738, all records of his birth are very likely lost to history.
I propose, rather, that my 6 GG Philip, born 1735 in Frederick, Maryland, and your William are brothers born to a Thomas Butler b. 1707 and Elizabeth Chere OR Chew b. Before 1715. I make the case on Philip’s profile page - at your convenience, please have a look: https://www.wikitree.com/wiki/Butler-10293
I've also posed this question to William's profile manager, but I would certainly love to hear your input.
If this is the case, the next brick wall would be James Butler, William's Grandfather. His death and land transactions are well documented, but his birth and/or immigration are not.