I am assuming that John Graham died between 1860 when such a person age 30 is listed with Anna age 24 and Arthur H age 2 in Nelson, Buffalo, WI and 1870 when a Arhthur Graham age 13 is listed with Jane Hodges age 33 and WC Hodges. I have death dates for Jane and WC (William Church) in Livingston, MI. But as you pointed out, no marriage for them.

My cursory glance at Wisconsin Civil War records found a Leutenant John H Graham in the 18th Wisconsin Infantry, but no death listed for him.
I had hoped that a newpaper article could be found for him. I have reviewed all of the places that you have listed.

Thanks for your help.