I have a complete inventory of all graves in the (Town of) Marion Cemetery which I am certain is the same cemetery as the Leach Corners Cemetery. My father and I visited there in September, 2000.
There are two children of Milo Leach and Eunice (Corse) Leach buried in the Marion Cemetery.
Frank E. Leach, died March 25, 1862 at age 4
Elmer E. Leach, died February 26, 1863 at age 22 days.
Clarence Edward (Ed) Leach and Mercy (Spurbeck) Leach had three children but I only have a date of death for one of them, Lyle, but he lived to adulthood.
My best guess is that the casket you speak of belonged to Frank E. Leach and that the funeral was held a month or so after he had died.