Tapp

I am working on my father's family. Herman Franklin Tapp born 3/24/1900 to William H Tapp born June 1856 and Mariah Ruth Ernest born September 1864. His parents were married in Illinois 9/29/1881. My father came from a large family - 

I am looking for death records for both of his parents. William died in Oklahoma between 1920 and 1930; Mariah, aka Ruthie in Phoenix Az mid to late 1940' I was about 4 years of age when she died.

I have been trying to find either church records, newspaper obits or vital records. Tried find a grave and billion graves with no luck so far.