I don't think you have enough evidence to make that assumption. I traced the Charles and Rosetta/Rosella Casey back to 1895 Jenings, Decatur, Kansas. He was listed as C N Causey and she as Rosetta Caisy/Causey.
IS Charles hardin Casey b. 1855 Schuyler Co., Illinois your ancestor? What were his parents names? Then move forward in time. Where was he living in 1860 and 1870?