At this time, I do not have definitive proof that William Riley Chaffin, younger brother of Eli Chaffin, and William Riley Chaffin, husband of Louisa Fleming, are actually the same person. But the clues point in that direction.
The web site of the Illinois State Archives [http://www.sos.state.il.us/GenealogyMWeb/landsrch.html] records 2 land purchases by Elias Chaffin (is it the same person?), one in GALLATIN Co. on 10/11/1819 (160 acres @ $2/acre), the other in MARION Co. on 04/05/1839 (40 acres @ $1.40/acre). Of course, if the date of death listed above is correct, that presents a little problem...