My Austin was born in 1831 in Johnstown Ohio and married a Mary unknown. They had had 4 children, Edwin, Mary, Sarah, and Austin ...all born between 1853 and 1859. My Austin is to be found as late as 1880 in Johnstown Ohio and his widow and some of the kids are still to be found in Ohio at a much later date. In 1870 Austin was in Hartford Township in Licking Co. Ohio.
I have wondered myself about your Austin... but have not been able to establish a connection. My line appears to have been very found of names that start with the letter A....and many of Josephs sons... did end up in Illinois and remained there until there deaths.... Austins brothers... Augustine, Alvi, Marvin... and many descendants of these brothers.
Searching the internet and Ancestry.com has seem to prove to me how few records exist for the name Austin Barnum in general. My Austin also has proved rather elusive. By profession he was blacksmith.
Hope you find your Austin. If I come across your Austin while searching mine -or vice versa... lets trade info. Good luck,
Christy