If the father-in-law was James Madison Poole 1835 - 1912 he is buried in Millwee Cemetery.
As far as I can tell they had statewide registration of deaths in 1914 - of course you still had spotty records up to about 1920- it would depend on the county I know Ft. Smith has some going back to 1881.
You can try the County Clerk in Sevier Co - if that is where you think they died.
County Clerk Court House DeQueen, AR 71832 (870) 642-2852
at least that is what they have on the Vital Records web site.