Smiths from Tennessee

im still looking for samuel smith. he was born 1842 in tennessee. he married i beleive malvina steel cropp in 1870 in dekalb alabama. if you have any information please let me know. it seems i have hit a major brick wall.
there is one son.james william smith born june 23 1871 in tennessee. any ideas how i could find his birth certificate????
thank you
jenny