1.  Marriage Record:

.  GED2HTML at www.foorgenealogy.com, which cites the following:

.  Author?  1891.  Portrait and Biographical Album of De Witt and Piatt Counties, Ill.  Chapman Bros., Chicago, p. 556.  [not seen]  Excerpt:

Mr. [Peter] Croninger was born March 2, 1818, in Pickaway Co., OH.  He is the only child surviving in a family of seven.  He lost his mother when he was very young, and his father, Peter Croninger, Sr., also died in Pickaway County.  The latter was a native of Pennyslvania and an early settler in Ohio.  One of his brothers, Leonard Croninger, was stolen by the Indians and reared by them, not being able to get away from the tribe until he was about 26 years old. In the fall of 1839 Mr. Croninger bought over 300 acres of land in Piatt County and paid $8 per acre therefor.  The following spring he came hither accompanying Isaac Faylor, the entire journey being made with a wagon and three horses and consuming perhaps nine days...

By 1891, all of Peter Jr.'s siblings had, indeed, passed away.  The romantic tale of his father having a brother, Leonard, may be just that, a tall tale, and it may refer to his grandfather, Leonard, rather than an alleged brother.