At the time your William Diehl was born (1809) West Buffalo Twp was part of Northumberland County.In the 1810 US Census the following Deals are found in W. Buffalo Twp.
West Buffaloe Twp –Alphabetized return p. 332 Philip Deal, farmer 2-2-0-1-01-2-0-1-0 Henry Deal, farmer 0-0-0-0-10-0-0-0-1 John Deal,Carpenter 1-0-0-1-01-0-1-0-0
Both John and Philip Deal have sons of the correct age to be fathers of William.Henry is older and could be the father of Philip and/or John (or neither). I'd start searching Northumberland and Union County records for more details on their families.Don't forget to be very liberal with your spelling (Dale-Deal-Deel-Diehl-Dill-Teal-Thiel, etc.).One early German family (Christian Diehl)that moved to the part of Northumberland County that later split off as Centre Co changed its name from Diehl to Dale. Ed Deal Researching PA Deal/Diehl families