Not sure that my William Rardin is the same as your William Henry Rardin, but this is what I have.
William Rardin's parents were Samuel Rardin and Melinda Fairbanks. I have him born in 1839 in Gilboa, Putnam County Ohio. I have his death date as 6 March 1905 in Waterville, Minnesota.
Most of this information was compiled by my late grandmother Edwytha Rardin Leibel. I am not sure where she got her information.
I did travel to Waterville earlier this year, and I found a courthouse record of his death certificate. According to the information on the death certificate, he is buried in the Waterville Twp cemetery, which I believe is the Sakatah cemetery. I have photos of all the Rardin graves there, but William is not one of them. I do have a few photos that I cannot see very well.
I hope this information is what you are looking for. You can reach me at email@example.com or at firstname.lastname@example.org if you want to email me.