The info I have about Josiah Downing is that he died within a few years of his marriage to Elizabeth Jones, and she proceeded to marry Michael Roseberry abt.1815.

Have you checked out the Madison County History of 1883?

Here are a couple of passages from the Madison Co History of 1883 that may be of help:

"p 628 we now reach the fall of 1806, in which year Rev Lewis Foster camefrom PA and took up the land prev built upon by Jonathan Alder. On this farm Francis Downing, son in law of Rev Foster, came in the fall of 1806 and settled near the present site of Foster Chapel. Francis Downing and wife had one child and in 2/07 had another, Jemima.......Of the Downing family, all moved to Indiana save Jemima, widow of the late Israel Brown......

p 634 Foster chapel sunday school class 1808:
Lewis Foster & wife
Joshua, John, Benjamin, Joseph Foster - sons of L Foster, and wives
Rebecca Tomilson
Cassa Dwyer
Joseph Downing
Frank Downing (bro of above) and their wives

p 640 Foster Chapel cem: 1823 Rachel Downing

P 1085 DAVID DOWNING BN ON THE LOWER GLADE MADISON CO 6/17/1853, SON OF ALBERT AND FRANCES DOWNING, HE A NATIVE OF FRANKLIN CO OH AND SHE OF LONDON, THIS COUNTY. GRANDPARENTS WERE TIMOTHY AND ELIZABETH DOWNING, OF SCOTCH DESCENT, AMONG FIRST SETTLERS ON THE LITTLE DARBY, PRIOR TO 1800. ALBERT HAS A BROTHER ISAAC H, A RESIDENT OF CALIFORNIA FOR 30 YEARS."

Hope this helps!