We know William or John William as John’s son from his presence in his father’s household in 1850 and 1860. He is linked to John as his father on find-a-grave. He is designated P5a1f.

John William’s wife was Wilhelmina (or perhaps Philamena) Geyer. They married 7 Oct 1862. I know that from their marriage record from Auglaize County records sent to me by their great-great-granddaughter Barbara Green.

There is a database of Ohio marriages on Ancestry.com based on a transcription of county records, so presumably the same source record. Inexplicably that transcription has 7 Jul 1861.

John William and his wife Philamena are on find-a-grave.

Barbara Green sent me this list of their children:

Josephine Sophia Henrietta Mertz Sheridan:  DOB 11-27-1882  DOD  7-11-1950
Benjamin Frank Mertz: DOB 11-20-1863  DOD         1896
Frederick Oliver:  DOB 9-9-1865    DOD 12-21-1950
Mary Louise Mertz Dixon:  DOB 3-19-1867    DOD 4-2-1941
Charles William Mertz:  DOB 3-8-1869   DOD     1945
Sarah Catherine Mertz Alberding:  DOB 4-6-1871  DOD 7-     -1921
Henry O. Mertz:  DOB 4-8-1872    DOD 1874
George W. Mertz:  DOB 2-5-1874    DOD 1-5-1958
James Albert Mertz: DOB 9-2-1878    DOD 8-17-1966
Emma Rebecca Mertz Wakefield: DOB 4-21-1881    DOD 5-     -1978
Jeanette M. Mertz McCall:  DOB 5-14-1883    DOD       -1961
Harry Mertz:  DOB 4-3-1886    DOD 3-14-1970

She was variously Mena or Philomena in Census but her marriage record says her name was Wilhelmina Geyer. Her tombstone says Philamena and her daughter Josephine named a daughter Philamena. I don’t know which version of her name is correct.