Harry's marriage in OKhttps://familysearch.org/ark:/61903/3:1:9Q97-Y33T-PD7?mode=g...
Since John is living with Harry 1900 OK, maybe an OK death cert might be helpful.
John wasn't in Belmont Co very long.
The 1850 census resides Guernsey Co; possibly it is he in 1860 Harrison Co.
The heaviest concentration of DAVIDSONs 1830-40 are in Harrison & Jefferson Cos
John either....orphaned, or apprenticed out. Kids are considered orphans if dad is dec'd, even if mom is still living. You may want to check into the WALLACE and NORRIS families for possible connection. You might check for guardianship records in Harrison and Guernsey Cos.
1910 his middle initial is H. At least 2 census he says mom b Ireland
1880 KS census says Mary is step-dau, but it looks like she is John's dau.
Name: John Davidson
Age in 1870: 25
Birth Year: abt 1845
Home in 1870: Kirkwood, Belmont, Ohio
Post Office: Hendrysburg
Value of real estate: View image
Mary Connor 46 [John's m/inlaw]
Jane R Connor 20
John W Connor 22
Emma Trimmer 24
John Davidson 25 <<-------------------
Mary A Davidson 1 <<-----------------------
Frank Dillem 58
Possibility....John m Margaret CONNER 1867https://familysearch.org/ark:/61903/3:1:9392-S5WW-5?mode=g&a...
Mary A DAVIDSON either died or married Douglas Co KS [listed 1880, not 1885]
That's about all I have to offer. Sometimes we just come to a dead end....I have several myself, even aft 40y of research.