Thanks for the info. I have found a William Fenkner that shows up in records in Minnesota and seems to have fought for the Union in the Civil War. I believe yours is probably the same. I also have a William that shows up in 1850 in a Lehigh County, PA census. He is 24, a chocolate-maker, and born in Germany.
William seems to be popular name among the Fenkners. The surname however is quite rare, I am finding.