between 1865 and 1901 of 8 post civil War Presidents it is said 5 were members of the Grand Army of the republic.
I have confirmed this is true for Grant; Hayes; Harrison and Mackinlay.
Reportably the Fifth was James Garfield; So far I found he made Speech on Memorial Day in May 1868 at Arlington National Cemetery and several GAR Chapters attended his Funeral in 1881.
Was he a member of the GAR Chapter near his home of Mentor, Ohio?
{I doing a possible book in the future for the Civil War]