He was named in his father’s will.

I went looking for John Hassinger’s sons in the 1850 Census. The only matching name I could find was David. He was the only David Hassinger living in Union County in 1850 -- which didn’t prove it was the same David mentioned in John’s will, but sure made him a good candidate. Turns out he lived in Middlecreek Township and he was buried at Salem Rowe’s -- just like his presumed sister. So this proximity strongly supports the notion that he and Mary Ann were brother and sister and that the John whose will mentioned a daughter Mary Ann and son David was in fact the father of our Mary Ann, wife of Benjamin Kramer.

Then I found an Ancestry family tree on-line -- never to be taken as fact but sometimes useful to point me in the right direction -- and it showed this same David (the same family members as indicated in Census) and said he was the son of John and wife Catherine and cited the same will I had found. It also tied John into the early Hassinger family that I knew something about but was never certain how John fit in.