I don't know if any of this will be new to you, but just in case. I am not related , only trying to help.
Since you have mentioned the 1880 census , I will not copy it in, except to say, the James A, listed was age 23 and a son of John A. Dean.
John A. Dean to Mary FergusonOct 5 1876Cass Co. IN
1870 census Cass Co. IN, image 23 162/161James A, Dean45Ohio (Error by census taker) Mary36Ohio John15 IN James 13" Olive 12" Ada10" William 8" Charles 6" Robert4" Mary1" John A. Dean to Mary A. Ballinger 20 Oct 1853 Miami Co IN.
1860 CassCo. IN image 19 863/852John A, Dean33farmerOHio Mary A.27Ohio John A5IN James W,4" Olive G.2" Addie J.3/12" Nancy Balinger 14IN Most likely step daughter
1850 Cass Co IN Image 2 16/16 John A. Dean24b OH Jane50PA No doubt mother and siblings James10IN Rosannah12" Hannah16" Elizabeth20OH Margaret18"
Some marriage in Cass County Indiana Ada J. Deanto Geo. I Veal1 Feb 1877 John E.to Hora Barnes20 nov 1886 Robert B.to Mary E. Jones 10 Apr 1888 William W.to Sallie W. Crimes Nov 13, 1879